FOUS11 KWBC 020854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 AM EST Sun Mar 2 2025

Valid 12Z Sun Mar 02 2025 - 12Z Wed Mar 05 2025


...California & Great Basin to the Central Rockies...
Days 1-3...

A closed upper-low tracking into California today will direct IVT=20
of ~300 kg/m/s at the southern Sierra Nevada and Southern=20
California ranges. While SWrly low-level winds may provide some=20
marginal upslope flow enhancement, this IVT is not particularly=20
strong, thus limiting most heavy amounts to the highest/more remote
elevations. Snow levels are expected to be as low as 4,000ft from=20
the Sierra Nevada on east into the Great Basin, but the heavier=20
amounts will generally be confined to elevations above 6,000ft.=20
Snow will fall heaviest over the Sierra Nevada and as far north as=20
the Shasta/Siskiyou through Sunday evening. As the upper low=20
approaches Sunday afternoon, Pacific moisture will spill over into
the Great Basin with moderate-to-heavy snowfall along the=20
6,000-7,000ft ridge lines of central Nevada Sunday afternoon and=20
into Monday. WPC probabilities depict moderate-to-high chances=20
(50-80%) for snowfall >8" at elevations above 7,000ft in the Sierra
Nevada through Monday morning. High chances (70-90%) for >6" of=20
snowfall exist along the ridges of central Nevada through Monday=20
evening.

The closed upper low will make its way into the Central Rockies on
Monday and eventually the Central Plains by Monday night. Falling=20
heights, strong jet-streak dynamics aloft, and residual Pacific=20
moisture will support moderate to locally heavy snowfall in the=20
Wasatch, Uinta, southern Wyoming Rockies, and northern Colorado=20
Rockies. WPC probabilities show moderate-to-high chances (50-80%)=20
for snowfall >8" at elevations above 9,000ft. Farther north,=20
temperatures will gradually cool as a cold front ushering in=20
Canadian high pressure moves south. Lingering Pacific moisture,=20
combined with weak easterly upslope flow will allow for light-to-=20
moderate snowfall in the Northern Rockies between Monday afternoon=20
and Tuesday morning. Most snowfall totals will range between 1-4"
with localized totals topping 4" in the peaks of the Big Snowy,
Little Belt, Lewis Range, Absaroka, and Big Horns.=20


...Central Plains to Upper Midwest...
Days 2-3...

...Powerful winter storm to inflict a plethora of dangerous weather
hazards from the Great Plains to the eastern U.S, including
blizzard conditions in the Central Plains...

The synoptic-scale evolution and primary features are generally=20
agreed upon by all guidance; a strong jet streak over northern=20
Mexico will place its highly divergent left-exit region over the=20
central Plains Monday night. Paired with strong PVA ahead of the=20
500mb low in the Rockies aloft will organize and strengthen a=20
surface low in lee of the Colorado Rockies as early as Monday=20
afternoon. Guidance seems to be in decent agreement on the position
of the upper low through 06Z Tuesday (ECENS slightly farther south
than the GEFS) and these ensembles will remain in these camps will=20
through 12Z Wednesday as the storm moves into the Midwest.=20
Interestingly, NAEFS/ECWMF SATs depict mean IVT surpassing the=20

97.5th climatological percentile over eastern CO early Tuesday=20

morning. This is a byproduct of the exceptional 500-700mb moisture=20
aloft that is associated with the deformation axis producing a=20
burst of heavy snow. This will focus the heaviest snow along the=20
Palmer Divide and southeast Front Range of southeast WY via strong=20
enough NErly upslope flow, along with stronger dynamic cooling=20
aloft to support heavier snowfall in the most elevated terrain
through Tuesday morning. These areas are also at risk for strong
wind gusts. The ECMWF EFI shows >0.8 values along the Palmer=20
Divide for snow and wind gusts, suggesting the potential for=20
significant impacts via those to weather hazards. Through 00Z=20
Wednesday, WPC probabilities show moderate-to-high chances=20
(40-70%) for snowfall >6" along the Palmer Divide and the Front=20
Range of southeast WY.

The snowfall potential east of the Rockies, however, will be=20
primarily tied to the deformation axis placement and dynamic=20
cooling aloft east of the Denver metro and points north and east.=20
This dynamic storm system is not working with an antecedent air-=20
mass that is overly cold/dry. That said, the changeover to snow=20
from eastern Colorado, southeast Wyoming, and into much of NE/KS=20
will coincide with considerable wind gusts that range between 50-70
mph in some cases. Snowfall amounts will vary in these areas and=20
are likely to be difficult to measure given the powerful winds. The
expectation is any snowfall (1-4" worth) combined with >50mph wind
gusts will likely result in blizzard conditions for motorists and=20
aviation. The WSSI-P shows a wide swath of 50-70% probabilities for
Moderate Impacts related to Blowing Snow alone from the Palmer=20
Divide and southeast WY on east through northwest KS, and through=20 west-central NE. This is likely to result in whiteout conditions,=20
power outages, and closures in affected areas on Tuesday.=20

By Tuesday evening, the storm continues to strengthen as it heads
for the Midwest. Intense vertical velocities beneath the TROWAL
will support dynamic cooling that forces precipitation to fall in
the form of snow Tuesday night from eastern Nebraska and northeast
Kansas on north through western Iowa and into the Upper=20
Mississippi Valley. Periods of heavy snow and whiteout conditions=20
are likely in these areas with heavy snow even stretching into the
Michigan U.P.. From Minnesota on east to northern Wisconsin and=20
the Michigan U.P., these areas are more at risk for heavy snow=20
thanks to a more aptly-timed cold frontal passage cooling the
boundary layer more effectively while also being co-located beneath
the TROWAL. Though 00Z Thursday, WPC probabilities depict=20
moderate-to-high chances (40-70%) for snowfall >6" from southeast=20
MN to northern Wisconsin and the central Michigan U.P.. The ECMWF=20
EFI depicts >0.8 values for heavy snow and wind gusts in these=20
areas. Expect significant travel disruptions are anticipated due to
the combination of heavy snow and high winds through Wednesday
afternoon.

WPC has initiated Key Messages for this powerful storm system. The
link to view the Key Messages are below.


Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!7cLHK2TMAm9ydtPin_-tnjoyqnnYVKAgIaRRx0dKCtpJm= tWub5O5OF70D-fTWDvP1OdUoXWYWfhYXPsZMaqfJCaTMCk$=20


$$

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FOUS11 KWBC 022047
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
347 PM EST Sun Mar 2 2025

Valid 00Z Mon Mar 03 2025 - 00Z Thu Mar 06 2025

...California & Great Basin to the Central Rockies...
Days 1-3...

A progressive but highly amplified upper level pattern will set up
across the country through the middle of the workweek. This highly
energetic pattern will support widespread wintry weather across=20
the Rockies. Starting tonight, a deep upper level trough will be=20
over California and the Great Basin, with instability induced by=20
the cold air aloft supporting widespread snow across many of the=20
local mountain ranges from the west coast to the Uinta Mountains of
Utah. The snow will spread east to the Front Range of Colorado by=20
Monday as the upper level trough pushes east and lee cyclogenesis=20
begins in eastern Colorado. Meanwhile, an upper level front will=20
follow behind the trough across the Pacific Northwest through=20
Tuesday morning. The front will provide the forcing for snow to=20
continue from Washington State east through Montana, while a=20
surface polar high over the Canadian Prairies provides cold air=20
from the north, keeping snow levels low (under 4,000 ft. in some=20
areas) from the Sierras north and east through Montana. Integrated=20
Vertical Transport (IVT) values through Tuesday will generally peak
between 200 and 300 kg/ms. These are modest values, implying that=20
at first, lack of available moisture will limit accumulations,=20
especially where orographic uplift is not present to wring out=20
additional snowfall. WPC Probabilities remain high (70-90%) for at=20
least 4 inches of snow through Monday afternoon across the ridges=20
of central and northeastern Nevada.

As the upper level low pushes east through Tuesday and the
developing Plains cyclone takes over as the primary forcing
mechanism for heavy snow, the probabilities of heavy snow will=20
also shift east into Idaho, Wyoming and Montana, as well as into
the Front and Park Ranges of Colorado. A shortwave embedded within
the upper level trough will locally increase upper level=20
divergence in the favorable left exit region of a 150 kt jet that=20
extends into west Texas. The low level jet will be strengthening=20
from east Texas into Arkansas, drawing Gulf moisture northward.=20
However, in these early stages of the low's development, moisture=20
into the northern half of the storm will still be limited. Thus,=20
the heaviest forecast snow totals will be limited to the Front and=20
Park Ranges and adjacent mountains where orographic uplift will=20
provide a larger fraction of the overall lift causing the heavy=20
snow. There is a moderate (50-70%) chance of at least 6 inches of=20
snow through Tuesday afternoon at 8,000 ft. and higher in the=20
latest WSSI-P. Further north and west across Wyoming and Montana,=20
where the upper level front will be the dominant forcing mechanism=20
and further away from the Gulf, snowfall totals will be lighter.=20
There is a low (10-30%) chance of 4 inches or more of snow in these
areas in the WPC probabilities.

A second deep trough in the upper level flow will move into the
West Coast on Wednesday, with yet another round of heavy snow
possible from the Sierras into northern Nevada through the day on
Wednesday. A surface low may develop to the lee of the Sierras
across southern Nevada as a result of the forcing and leeside flow
over the Sierras. The timing of how fast the cold air can fill in
behind (north and west) of the low, as well as the extent of the
precipitation shield will be critical as to potential snowfall
accumulations. There remains considerable uncertainty about those
factors, which will become more clear with future updates in the
guidance.

...Central Plains to Upper Midwest...
Days 2-3...

...Powerful winter storm to cause widespread heavy snow and blowing
snow with localized blizzard conditions across the central Plains
from Monday night into Tuesday and then into the upper Midwest
Tuesday night through Wednesday...

The upper level trough that ejects from the Rockies into the Plains
Monday night will have an embedded low that moves across Colorado
and into Kansas. This will be the focus for where the surface low
will form and rapidly intensify during the day on Tuesday. The
trough will become negatively tilted Tuesday, resulting in a
steadier intensification of the surface low as it tracks northeast
from Kansas to northern Michigan by Wednesday evening. North and
west of this track, from northeastern Colorado to western Iowa,
southern Minnesota, Wisconsin, and northern Michigan, a period of
heavy snow is likely as the comma-head of the storm moves over the
region. Meanwhile, the surface low will deepen well into the 980s
hPa range. With a polar high providing cold air and adding to the
baroclinic instability with the remarkably strong LLJ pumping Gulf
moisture northward ahead of the storm, very strong winds will
accompany the heavy snow, causing widespread blowing snow and=20
possible blizzard conditions.

The latest WPC Winter Storm Severity Index (WSSI) shows a large
area of Moderate impacts (disruptions to daily life, with extra
caution needed while driving) through Wednesday morning from the
northeast corner of New Mexico north across almost all of the=20
eastern Colorado Plains, the western two-thirds of Nebraska, and
south-central South Dakota. This is being driven almost entirely by
the blowing snow component of the WSSI. Due to both the intensity
of the storm and its fast movement, there will be a rapid
transition of precipitation-type from rain to snow on the west/cold=20
side of the storm. Also due to the strong winds and resultant
blowing snow, there is considerable uncertainty as to snowfall
amounts from the Plains to the U.P. of Michigan, as blowing and
drifting will cause large variability in accumulations from place
to place. Thus, for most areas, expect the impacts from blowing
snow to outweigh the impacts from snow amounts alone. Further, the
high winds will likely break apart any larger snowflakes, resulting
in lower SLRs and lower accumulations, but increasing the number of
partial flakes in the air and contribute to lower visibilities.

There is likely to be an area of lower accumulations in and around
eastern Nebraska as the low refocuses and develops. This will occur
when the upper level trough supporting the low first turns
negatively tilted Tuesday afternoon, and the southern jet streak
rounding the base of the trough extends far enough northward ahead
of the trough to maximize the upper level divergence by Tuesday
evening between that jet streak and a second west-east oriented
jet streak extending from the Arrowhead of Minnesota east across
the Canadian Provinces of Ontario and Quebec.

Wegman

...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9ymDF-SiR9avKm5oo18FacgpBrzO1VrsXnyLWbfEnxXSE= uS_wwBDEPVdPZHI2oXGji43XcNKqdSsY2eVrLdABwXYd-w$=20

$$

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FOUS11 KWBC 030833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 AM EST Mon Mar 3 2025

Valid 12Z Mon Mar 03 2025 - 12Z Thu Mar 06 2025

...Great Basin to the Central Rockies...
Days 1-2...

A potent 500mb closed upper-low barreling through the=20
Intermountain West will generate exceptional divergence aloft while
modest 700-300mb moisture wraps around the northern and western=20
flanks of the closed low. The result is high elevation snow from=20
central Nevada on east through the Wasatch, the Uinta, as far south
as the Mogollon Rim, and east to the southern Wyoming and Colorado
Rockies. WPC probabilities show high chance probabilities (>70%)=20
for snowfall >6" in the Nevada ranges above 6,000ft, the Utah=20
ranges above 8,000ft, and northern Arizona ranges above 7,000ft.=20

By 00Z Tuesday, the 500mb low tracking across southern Colorado
will work in tandem with the divergent left-exit region of a
250mb jet streak to support lee cyclogenesis over the central High
Plains. As the closed low aloft strengthens at 700mb and 850mb, a
strong 50+ knot LLJ will direct a stream of low-level moisture
northward through the Southern Plains that wraps around the
700mb low. The northerly flow with embedded moisture aloft is
strong enough to the point that by 12Z Tuesday, there is a=20
northerly >200 kg/m/s IVT over eastern Colorado. This anomalous=20
moisture source, combined with the robust synoptic-scale=20
enhancement will support heavy snow in the Front Range of the=20
Colorado and southern Wyoming Rockies, and as far south as the=20
Palmer Divide. The Palmer Divide in particular is particularly at=20
risk for blizzard conditions Monday night into Tuesday morning as=20
700mb winds of 50-70 knots result in whipping wind gusts. WPC=20
probabilities show high chance probabilities (>70%) for snowfall=20

8" in the northern Colorado Rockies above 9,000ft. Along the

Palmer Divide, WPC probabilities show moderate-to-high chances
(50-70%) for snowfall >6" through Monday evening. Snow should=20
taper off around midday Tuesday along the Front Range of the=20
Rockies.


...Central Plains to Upper Midwest...
Days 1-3...

...Powerful winter storm to cause widespread heavy snow and blowing
snow with localized blizzard conditions across the central Plains
from Monday night into Tuesday and then into the Upper Midwest=20
Tuesday night through Wednesday...

By 06Z Tuesday, a closed and potent 500mb low will track into
western Kansas with a rich plume of low-level moisture advected
northward by a >50kt LLJ over the Southern Plains. Moisture will=20
wrap around the deepening cyclone, resulting in strong 850-700mb=20
WAA that causes a narrow axis of moderate snow embedded within a=20
wind field that could produce >70mph wind gusts late Monday night=20
and into Tuesday morning. The upper-low takes a subtle dip south=20
and east along the KS/OK border midday Tuesday before tracking=20
northeast towards the Midwest Tuesday evening. The 700mb will will=20
track over the Kansas City metro by 00Z Wednesday and the pivoting=20
axis of best 850-700mb FGEN will pivot from eastern Nebraska and=20
northeast Kansas on northeast through Iowa and into the Upper=20
Mississippi Valley. The enhanced mesoscale forcing will be co-=20
located beneath a "kissing jets" setup; where the developing storm=20
system lies beneath the divergent left-exit region of a jet streak=20
over Texas, and beneath a strengthening jet streak over the upper=20
Great Lakes. Plus, 850mb and 700mb heights at this time over
eastern Kansas are below the observed heights for this time of year
in the CFSR climatology. With robust ascent aloft and strong=20
mesoscale forcing within the deepening TROWAL, the deformation axis
of heavy snow will be capable of producing up to 1"/hr snowfall=20
rates and whipping wind gusts of 50mph. While the band will be=20
progressive as it moves through eastern Kansas and eastern=20
Nebraska, that 3-6 hour wind of heavy snow can still cause=20
significant reductions in visibilities for motorists and aviation=20
Tuesday evening.

The storm then tracks through eastern Iowa Tuesday night with its=20
expansive deformation axis producing snow from the Kansas/Missouri=20
border on north through central Iowa and as far north as the=20
Michigan U.P.. Strong wind gusts topping 40 mph are possible in=20
these areas Tuesday night and into Wednesday. The heaviest snowfall
by Wednesday morning will be found across southeast Minnesota,=20
northern Wisconsin, and the Michigan U.P.. The Michigan U.P., in=20
particular, is most favored for heavy snow due to the help of=20
lake-enhanced snowfall and colder boundary layer temperatures.=20
Snowfall will be more difficult to accumulate during the day=20
Wednesday on the fringes of where it is snowing rather than beneath
the heaviest rates, but the blustery wind gusts still can cause=20
near whiteout conditions in some cases. In addition, the high=20
moisture content and lower SLRs from central and northern Wisconsin
to the Michigan U.P. suggests the combination of a heavy/wet snow=20
on trees and power lines could lead to some cases of power outages=20
and downed tree branches.=20

WPC probabilities shows moderate chances (40-60%) for snowfall >4"
from western and northern Nebraska to southern South Dakota. There
is then another swath of moderate-to-high chance probabilities
(40-70%) for >4" of snowfall from eastern Nebraska to northern
Iowa. Southern Minnesota on north and east through northern
Wisconsin and the Michigan U.P. sport 50-70% odds of snowfall
totals >6". There are some low chance probabilities (10-30%) for
localized snowfall totals >12" in parts of far northern Wisconsin
and along the Michigan U.P.. Overall, blowing snow will be the
most detrimental impact from the central High Plains to central=20
Iowa and southern Minnesota, while snow amount, snow load, and=20
blowing snow all make for a treacherous day of travel in portions=20
of the Upper Mississippi Valley Tuesday night and through=20
Wednesday.

...California, Great Basin, & Intermountain West...=20
Day 3...

Guidance is in agreement on an approaching upper-level trough off
the California coast that will interact with the subtropical jet in
the East Pacific. This interaction will produce a strengthening IVT
that tops out around 400 kg/m/s IVT at 12Z Wednesday and directs
its moisture well into the Southwest U.S.. By 00Z Thursday, the=20
IVT and its broad >200 kg/m/s footprint extends into the Wasatch=20
and Central Rockies. As the upper trough takes on a more negative=20
tilts along the California coast Wednesday afternoon and eventually
over the Great Basin Wednesday night, heavy snow will gradually=20
descend along the spine of the Sierra Nevada and into central=20
Nevada as well. WPC probabilities show high chances (>70%) for >12"
of snowfall at elevations above 9,000ft in the southern Sierra=20
Nevada with similar high-chance probabilities for >8" of snowfall=20
in the central Sierra Nevada. WPC probabilities also show some=20 moderate-to-high chance probabilities (50-80%) form snowfall totals

4" in central Nevada on east to the Wasatch and Uinta through 12Z

Thursday. Periods of snow are forecast to continue across the=20
Intermountain West into Thursday.


Mullinax


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_S99kqepjj8tQGohwbg5c9-HCBK00NaCVbY8RPp8iRNkO= V_HifVsumpI6KzDNmhmO7JYjaOq6q9KXmxEr8BSuvMmZaI$=20

$$

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FOUS11 KWBC 032041
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
341 PM EST Mon Mar 3 2025

Valid 00Z Tue Mar 04 2025 - 00Z Fri Mar 07 2025

...Central Rockies and High Plains to the Upper Midwest...=20
Days 1-3...

...A powerful storm will move into the central U.S. tonight=20
Tuesday, producing multiple hazards through Wednesday, including=20
periods of heavy snow from the central High Plains to the northern=20
Great Lakes, as well as blizzard conditions across parts of the=20
central Plains and strong winds throughout the Plains...=20

A deep upper low is forecast to continue its track across the
western U.S., rolling out from the central Rockies into the High
Plains tonight. Snow will continue to spread across the central
Rockies, with several more inches likely across the western to
central Colorado ranges before diminishing on Tuesday.=20

Meanwhile, rain changing to wind-driven snow is expected to=20
develop on the backside of the surface cyclone deepening over=20
eastern Colorado this evening. Increasing low level moisture=20
advection into an area of strong ascent afforded in part by low-=20
to-mid level frontogenesis, upper jet forcing, and orographic=20
ascent will support the development of heavy snow along the=20
northwestern to western extent of the low -- impacting areas from=20
the Colorado Palmer Divide northeastward through portions of=20
western Nebraska and into parts of western and central South Dakota
tonight into Tuesday. While marginal temperatures may keep=20
accumulations in check at the onset, heavy rates (1-2+ in/hr) after
the changeover to snow is expected to produce areas of locally=20
heavier amounts, with WPC guidance showing higher probabilities (=20
greater than 50 percent) for accumulations of 4 inches or more=20
across portions of the region. Low-to-mid level frontogenesis will=20
help extend a stripe of rain changing to snow further to the=20
northeast through eastern South Dakota into central Minnesota, but=20
guidance indicates snowfall accumulations across those areas will=20
remain light through 00Z Wednesday.

By late Tuesday, guidance shows a deep, nearly vertically-stacked
low moving moving into the lower Missouri and mid Mississippi
valleys. Models show a powerful low level jet drawing moisture into
an area of strong ascent generated by a coupled upper jet and low-
to-mid level forcing. Dynamic cooling will support rain changing=20
to snow, with some guidance indicating heavy snowfall rates of 1-2=20
in/hr quickly developing within the associated comma head as it=20
extends from portions of eastern Kansas and western Missouri to=20
southern Minnesota and Wisconsin late Tuesday into Wednesday. The=20
models have trended wetter and colder in some areas, especially=20
across parts of the lower Missouri valley, resulting in an uptick=20
in probabilities for heavier accumulations.

Influenced by an amplifying northern stream trough to its
northwest, the storm is forecast to turn to the northeast, with
heavy snow continuing to develop on its northwest side as it moves
from the mid Mississippi Valley Tuesday night to the northern Great
Lakes by late Wednesday. Strong forcing and moisture advection=20
pivoting across southeastern Minnesota into central Wisconsin is=20
expected to contribute to some of the higher storm totals, with WPC
guidance showing high probabilities for accumulations greater than
6 inches across the region. Otherwise, WPC guidance indicates the=20
heaviest amounts are most likely to fall across parts of northern=20
Wisconsin and Upper Michigan, where the initial swath of=20
synoptically driven snow, followed by lake effect showers will=20
likely contribute to totals exceeding a foot in some locations.=20

Even for areas where heavy snow does not occur, powerful winds will
become a concern throughout much of the Plains into the Midwest,
gusting to over 70 mph in some locations. Snow combined with wind
will result in reduced visibility, with blizzard conditions likely
to develop in some areas, especially across portions of the=20
central Plains into the lower Missouri Valley on Tuesday.
=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 2-3...

A mid-to-upper level shortwave pivoting east ahead of a low=20
dropping south from the Gulf of Alaska is expected to tap deeper=20
Pacific moisture as it approaches the West Coast, drawing it=20
across central into southern California beginning Wednesday=20
afternoon, before directing it further south and east into the=20
Southwest and Great Basin. Heavy snow will initially focus across=20
the central to southern Sierra Nevada (above 9000 ft), where=20
favorable upper dynamics in addition to orographics will=20
contribute to higher rates. Then by late Wednesday and continuing=20
into Thursday, the threat for heavy mountain snow will spread=20
across the Great Basin, northern Arizona, and into the central=20
Rockies. In addition to the Sierra Nevada, the greatest threat for=20
snow amounts of 6 inches or more will include the Nevada, Utah, and west-central Wyoming ranges.=20

Pereira


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4XMbcBhpH_2iDxhy-MFbqZz3YgQGbvJ799_98q-RueYF_= 4PEuZgiAA9ztTYWZTAYBH4Fa4D_qFimoA_t2djfJtZDunA$=20

$$

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FOUS11 KWBC 040840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Tue Mar 4 2025

Valid 12Z Tue Mar 04 2025 - 12Z Fri Mar 07 2025

...Central Rockies and High Plains to the Upper Midwest...=20
Days 1-2...

...A powerful storm moving into the central U.S. will produce=20
multiple hazards through Wednesday, including periods of heavy snow
from the central Plains to the northern Great Lakes, as well as=20
blizzard conditions across parts of the central Plains and strong=20
winds throughout the much of the nation's heartland...=20

A powerful winter storm takes center stage today with periods of
snow and whipping wind gusts producing blizzard conditions in parts
of the central High Plains this morning. A clue to identifying how
powerful a storm is; reviewing the NAEFS/ECMWF situational=20
awareness tools and seeing each variable (temperatures, winds,=20
moisture, pressure, vapor transport) all either in the "max" or=20
"min" categories. By 12Z Tuesday, the storm's 700mb and 850mb=20
heights over western Kansas will be near the lowest in the observed
CFSR climatology, while mean specific humidity at the 500-700mb=20
layers are also above the 90th percentile. Periods of snow will=20
envelope portions of eastern CO (including as far west as the Front
Range and Palmer Divide), western and central Nebraska, and=20
western Kansas where wind gusts may exceed 70mph in some cases.=20
This will result in blizzard conditions that make travel by road=20
and air very difficult due to whiteout conditions. WPC=20
probabilities show low chances (10-30%) for snowfall >4" in=20
northwest Kansas and southwest Nebraska, but they jump up to=20 moderate-to-high chances (50-70%) over north-central Nebraska. Snow
should taper off by Tuesday afternoon but lingering strong wind=20
gusts are likely to linger through Tuesday evening.

As the storm marches west towards eastern Kansas Tuesday=20
afternoon, the mean 250-500mb trough axis will take on a negative
tilt that provides excellent diffluent flow aloft over the Midwest.
Plus, a classic "kissing jets" setup; denoted by the divergent
left-exit region of a jet streak over Texas and the divergent
right-entrance region of a jet streak positioned over the upper
Great Lakes. As strong 850-700mb warm air advection (WAA) pivots=20
north and west around the storm and anomalous moisture content
rotates around the 700mb low, a TROWAL will support intensifying
precipitation rates and lead to a narrow band of heavy snow that
originates over eastern Nebraska and northeast Kansas Tuesday=20
evening. The newest 00Z HREF guidance suggests the potential for=20

1"/hr snowfall rates within this band that could stretch as far=20

south as the Kansas/Missouri border. There are some hi-res
soundings do do show some elevated instability aloft that may lead
to thundersnow within this band. Farther north, the same slug of=20
moisture over northern Iowa, southern Minnesota, western and=20
norther Wisconsin, and the Michigan U.P. will also transition to=20
snow Tuesday night with >1"/hr rates possible there as well.=20
Combined with the strong wind gusts in excess of 40 mph, especially
along the Missouri River Valley on east into central Iowa,=20
blizzard conditions are possible in these areas Tuesday night. WPC probabilities shows western Iowa and directly along the Missouri
River on south to far northeast Kansas as having moderate chances
(40-60%) for snowfall >4". However, should the band pivot long
enough over the region, localized amounts of 6-8" are possible.=20

The heaviest snowfall is likely to occur from northern Iowa and
southeast Minnesota to northern Wisconsin and the Michigan U.P..
This is where the 850mb FGEN will be sticking around the longest,
while also being ideally placed beneath that 250mb jet streak's=20
divergent right-entrance region. Some lake-enhancement and upslope=20
component into the more elevated terrain of northern Wisconsin and=20
the Michigan U.P. will help to sustain periods of heavy snow into=20
Wednesday evening. The storm will be a quick mover and snow across=20
the Upper Midwest will be out of the picture by Thursday morning.=20
WPC probabilities now depict high chances (>70%) for snowfall total

12" from the Hurons of Michigan's U.P. on west to the Michigan=20

U.P.northern Wisconsin border. The Huron Mountains actually have=20
moderate chances (40-60%) for snowfall totals surpassing 24" for=20
the event. Farther southwest, WPC probabilities show moderate-to-=20
high chances (50-70%) for snowfall >8" from far northern Iowa to=20
the Mississippi river dividing southeast Minnesota and western=20
Wisconsin. With the combination of heavy snow and blustery winds,=20
there is the concern for heavy/wet snow weighing down tree branches
and power lines that could result in tree damage and power outages
from southeast Minnesota to the Michigan U.P..

=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 2-3...

An approaching upper rough off the California coast will interact
with the subtropical jet in the East Pacific. This interaction will
produce a strengthening IVT that exceeds 400 kg/m/s and stretches=20
as far inland as the Lower Colorado River Basin. ECMWF SATs show
the >400 kg/m/s over portions of the Desert Southwest topping the=20
99th climatological percentile by 00Z Thursday. This IVT will
introduce rich subtropical moisture into northern Arizona, much of
Utah, and into the central Rockies. At the same time, the
approaching upper trough will induce strong vertical ascent over
the Intermountain West. By 12Z Thursday, a closed 700mb low over
southern Idaho will become elongated to the east and develop
another 700mb low in lee of the Rockies by Thursday afternoon. The
track of the 700mb low places much of Wyoming in a favorable spot
for heavy snow, especially from the Tetons to the Wind River,
Medicine Bow, and Laramie Ranges. This developing storm in the
central High Plains will generate strong WAA at low-levels that
cause 850-700mb FGEN from eastern Wyoming to as far east as the=20
Missouri River early Friday morning. Details on snow amounts east
of the Rockies are not as clear, but additional snowfall is growing
in confidence north of I-80 across the Sand Hills of Nebraska with
lighter amounts closer over the western Corn Belt.

When it comes to areas with the best odds of seeing >18" of
snowfall, the southern Sierra Nevada and peaks of the Wasatch are
the better bets. WPC probabilities show moderate-to-high chances
(50-70%) for >18" of snowfall at elevations above 9,000ft in the=20
southern Sierra Nevada, while the central and Sierra Nevada are=20
more likely to see 6-12" above 6,000ft. Farther east, mountain=20
ranges such as the Uinta, Bear River, Teton, Wind River, Medicine=20
Bow, and Laramie have moderate-to-high chances (40-70%) for=20
snowfall >12". Even the lower elevations of Wyoming, as low as
4,000ft in eastern Wyoming have high chances (>70%) for >4" of
snowfall through 12Z Friday.

Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9ICMgntx5YBtPe5VJ6b1b2yF5S71x8O1mj3IP1esLAkZW= clygV_lL6ckKBLcruADYdf05y6POSOYAXjaTKVnJsHWlMw$=20

$$

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FOUS11 KWBC 041921
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EST Tue Mar 4 2025

Valid 00Z Wed Mar 05 2025 - 00Z Sat Mar 08 2025

...Central Plains through the Great Lakes and into the Northeast...
Days 1-3...

...Powerful storm to bring blizzard conditions to portions of the
Central Plains and Upper Midwest...

A rapidly strengthening surface low pressure is clearly evident on
the WV imagery this morning across the Central Plains, and it is
this feature which will bring a powerful blizzard to portions of
the country through mid-week. This surface low will traverse
northeast and begin to occlude tonight as the anomalous upper low=20
(850-700mb height anomalies falling to nearly -5 sigma and below
the minimum in the CFSR climatology according to NAEFS) stacks
vertically and crawls northeast, reaching the Great Lakes by=20
Wednesday aftn. Later Wednesday, this upper low will begin to fill
and open into a negatively tilted trough, ejecting into Ontario
Thursday morning, pushing the attendant cold front and accompanying post-frontal trough eastward through the Mid-Atlantic and
Northeast.

The intensity of this upper low will help sharpen a jet streak
which will rotate through the base of the trough and then lift
meridionally from near the Gulf states, placing the favorably
diffluent LFQ atop the best height falls to result in maintaining
strength of the surface low. This impressive synoptic ascent will
also help to draw significant moisture northward from the Gulf, as
an arc of PWs above the 97.5 percentile surges northward into the
Upper Midwest. This moisture will push north within enhance
isentropic ascent, and this is progged to lift into an impressive
TROWAL, especially from IA through the Great Lakes on D1 /Tuesday
night into Wednesday/. This TROWAL is likely to overlap with a
strengthen deformation axis collocated with strong frontogenesis=20
and a deepening DGZ (SREF 100mb depth probabilities 30-50%)=20
suggesting a stripe of heavy snow is likely from NW MO through the=20
western Great Lakes. This is additionally supported by the WPC=20
prototype snowband tool indicating nearly a 100% chance of 1-2"/hr=20
snowfall rates within this band.

Significant moisture, plentiful ascent, and a deep low pressure all
indicate that an impressive swath of precipitation will spread from
the Central Plains through the western Great Lakes D1, with the
primary challenge being where the snow/rain line will setup.
Guidance suggests the precip will begin as rain along and southeast
of a line from near Marquette, MI, to Minneapolis, MN, through all
of Iowa and into eastern KS. However, as the low continues to
deepen and pulls east, the resultant CAA combined with the
ageostrophic flow into the low will transition rain to snow
quickly, with the heavy snow then collapsing east through
Wednesday. The heaviest snow accumulations will occur within this
collapsing band of snow, and although amounts aren't expected to be
extreme, impressive winds of more than 50mph will create major
impacts due to blizzard conditions from snow that has a high chance

70%) of exceeding 6 inches from far NW Iowa through the Twin

Cities of MN and into the western U.P of MI. Locally 12+ inches of
snow is likely in the U.P.

As the low fills and moves more rapidly to the northeast and into
Canada D2, the attendant cold front and post-frontal trough will
race eastward producing a period of strong CAA on NW flow in its
wake. This will likely result in periods of moderate to at times
heavy snow, especially in the favored upslope regions in the
Central Appalachians and Adirondacks. WPC probabilities for more
than 4 inches of snow as moderate (30-50%) in the Central
Appalachians, and 30-50% for 2+ inches along the Chautauqua Ridge
and into the Tug Hill Plateau/Adirondacks.

This system has prompted the issuance of Key Messages which are
linked below.

Then during D3 /Thursday night and Friday/ another potent surface
low will emerge from the Central Rockies and race eastward as it
becomes embedded within more confluent downstream flow towards the
Ohio Valley. Ridging immediately downstream of this feature will
somewhat limit moisture return from the Gulf, and the accompanying
mid-level wave is progged to weaken rapidly into the flatter flow
east. Despite that, a swath of heavy snow north of the low track is
expected as some strung out 700-600mb fgen aligns west to east to
enhance ascent from Nebraska through Iowa and potentially as far
east as lower Michigan. There is considerable uncertainty and
spread with both the timing and intensity of this second low,
leading to lower confidence in the footprint of snow and resultant
impacts. However, at this time, WPC probabilities for more than 4
inches of snow peak around 50% in northern Nebraska.

=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 1-3...

A progressive upper level trough will move into the West Coast
Wednesday afternoon, then reorganize over the Rockies through
Friday. As it reorganizes, its forward motion will slow
considerably, allowing cold air to pool over the West as Pacific
moisture advects into the region, resulting in areas of heavy snow.
Multiple embedded shortwaves will rotate around the trough, which
will support more widespread snow over several Western states. On
Wednesday, a pair of jet streaks will further enhance the lift over
California, with the southern Sierras in both the left exit region
of one and the right entrance region of another. Ahead of the=20
upper level trough, a surface cold front will move south and east=20
off the Pacific and into the West Coast. The front will have a=20
limited tropical connection, increasing the moisture flux into
southern California. IVT values will peak around 400 kg/ms. That=20=20
Pacific moisture will rising into the 99th percentile compared to=20 climatology as it moves into southern California on Wednesday. As
this moisture pushes inland, the southern Sierras will get the
first opportunity to uplift that moisture in the form of heavy
snow. WPC probabilities are the highest in this region, with a
moderate (40-60%) chance of 18 or more inches of snow.

As the trough moves inland, the moisture moving northeastward ahead
of it will cause widespread mountain snow and valley rain and snow
across much of the Intermountain West through Thursday. A surface=20
low will develop over northeastern Nevada and move across Utah and
southern Wyoming through Thursday in response to the forcing from
the upper level trough and embedded shortwaves. The trough will
become more consolidated as an upper level low tries to form within
it on Thursday. This will increase the divergence in the left exit
region of the jet which will have moved into the Four Corners
region on Thursday. That jet streak will have embedded winds over
130 kt, so it will have plenty of energy for that surface low to
work with. The highest probabilities through Thursday night east of
the Sierras will be across the Uintas of northeast Utah and the
Wind River Range of central Wyoming, where there's a high (70-90%)
chance of 8 inches or more of snow. Lower (20-50%) chances of 8
inches of snow extending in a broad swath of the West from Nevada
northeast through Colorado and Wyoming, including some lower
elevations. Colder air associated with the trough will get time to
settle as the upper level trough/low stalls and reorganizes.

A surface low will develop over the Colorado Plains Thursday
evening. This low will take over as the primary forcing for the
heaviest snow as the snow shifts east across Nebraska along with
the low. By Friday morning, all organized heavy precipitation will
have moves east and out of the region. A secondary small low may
cause a brief burst of heavy snow over northern Arizona during the
day Friday for the higher elevations along the Mogollon Rim.


Weiss/Wegman


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9y3rk78-ESVyfVyZSn0RnaS3hhf461rndehwc1MyvDbjI= hQmIT_XkiLOZ4gRAoHYvdbmJ2AjgEl-pdNk001fatWLN4c$=20

$$

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FOUS11 KWBC 050906
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Wed Mar 5 2025

Valid 12Z Wed Mar 05 2025 - 12Z Sat Mar 08 2025

...Upper Midwest through the Great Lakes and into the Northeast...
Days 1-3...

...Powerful storm to bring blizzard conditions to portions of the
Upper Midwest...

The powerful winter storm continues to produce heavy snow and
blizzard conditions in some cases from northwestern Missouri
through the Upper Mississippi Valley this morning. This deformation
axis of snow, placed beneath the TROWAL and the right-entrance
region of a robust 250mb jet streak over southern Canada, will
support a band of snow generating 1-2"/hr snowfall rates. The
storm will track over the Wisconsin/Illinois border through late
morning with the swath of snow moving across most of Wisconsin and
the Michigan U.P.. Persistent NErly flow over Lake Superior will
keep periods of snow in the forecast across the Michigan U.P.
through Wednesday evening, but snow should finally taper off by
Thursday morning. Note that some periods of snow are expected on
the backside of the storm on Thursday downwind of the usual snow
belts of Lakes Erie and Ontario, as well as down the spine of the
Appalachians. Light snow totals will linger into Friday as well,
especially in the Tug Hill, Adirondacks, and the Whites. Most=20
snowfall amounts in these areas are likely to range between 1-4"=20
with some localized amounts approaching 6" in the Tug Hill.=20

WPC probabilities show moderate-to-high chances (50-70%) for
additional snowfall totals >12" in the Huron and Porcupine
Mountains along the Michigan U.P. Meanwhile, there are high chance probabilities (>70%) for additional snowfall totals >4" from
northern Iowa to southeastern Minnesota and western Wisconsin. Some
additional localized amounts of 4-6" are possible in west-central=20
Iowa on the back side of the storm through this morning. Expect
hazardous travel conditions in these affected areas, especially in
areas under blizzard warnings where visibilities may be near zero.

=20
...California, Great Basin, Southwest, and central Rockies...=20
Days 1-3...

An approaching upper trough off the California coast will interact
with the subtropical jet in the East Pacific. This interaction will
produce a strengthening IVT that exceeds 400 kg/m/s and stretches
as far inland as the Lower Colorado River Basin. ECMWF SATs show=20

400 kg/m/s over portions of the Desert Southwest that are topping

the 99th climatological percentile by 00Z Thursday. This IVT will
introduce rich subtropical moisture into the Great Basin and
Central Rockies. At the same time, the approaching upper trough
will induce strong vertical ascent over the Intermountain West. By
12Z Thursday, a closed 700mb low over southern Idaho will become
elongated to the east, developing another 700mb low in lee of the
Wyoming Front Range by Thursday afternoon. the track of the 700mb
low places much of Nevada, southern Idaho, and Wyoming in a
favorable position for heavy snow, especially from the Absaroka,
Tetons, and Wind River ranges to the Medicine Bow, Big Horn, and
Laramie Mountains. As the 700mb low stalls over the Tetons and Bear
River Range, a secondary shortwave trough revolving beneath the
longwave trough over the West will sustain a >200 kg/m/s IVT
directed at the southern Rockies. In addition to the upper-level
ascent out ahead of the upper trough, falling heights and lowering
snow levels will support periods of mountains snow along the
Mogollon Rim, the San Juans, the Sangre de Cristo, and the Front
Range of the Colorado Rockies. The snow in the Front Range and
Sangre de Cristo is a byproduct of upslope flow with low pressure
developing over the southern Plains and high pressure over the
northern Plains.

WPC probabilities show high chances (>70%) for snowfall exceeding
12" in the Sierra Nevada above 6,000ft, the >7,000ft ridge lines in
the Nevada, the Wasatch, Uinta, Tetons, Wind River, Laramie, and
San Juan ranges. Some portions of the Sierra Nevada, Wasatch, and
Uinta sport moderate-to-high chances (50-80%) for snowfall >24"
through Friday. Mountains of southern Idaho, the Absaroka, and the
Big Horns also have high chances (>70%) for snowfall >8" through
Friday. Much of the Mogollon Rim above 6,000ft are forecast to see
any where from 6-12" of snowfall. Some of the valleys in Wyoming=20
can also expect as much as 6-12" of snowfall through Friday=20
morning. The WSSI range from Moderate to Major Impacts with the=20
Major Impacts confined to the highest elevations of the mountain=20
ranges listed.


...Central Plains...
Days 2-3...

By Thursday, as the upper trough in the West aids in the
development of low pressure in lee of the Rockies, strong 700mb WAA
will foster 700mb FGEN over southeast Wyoming and Nebraska. A band
of heavy snow will stretch across these areas, including the Black
Hills and Sand Hills Thursday afternoon. Snow in these areas will
continue Thursday night and should taper off by Friday morning.=20
Some measurable snow may make it as far south as northeast Colorado
and possibly into the Midwest Thursday night into Friday, but=20
guidance suggests milder boundary layer temperatures may make it=20
tougher for much more than minor snowfall totals. WPC probabilities
show moderate-to-high chances (50-70%) for snowfall >6" in the
eastern Wyoming High Plains, the Black Hills, and northwest
Nebraska. Low chances (10-30%) for >4" of snowfall extend as far
east as east-central Nebraska.=20

Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_FIk615MMQwmdbhpmum_q_7cfCr5UpQMXSTW_emsmb3KI= 2JYJHc_zFFLDg9S0EeZ5n43YxgAZm49EcPxvumrAI6duMk$=20

$$

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FOUS11 KWBC 051904
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
204 PM EST Wed Mar 5 2025

Valid 00Z Thu Mar 06 2025 - 00Z Sun Mar 09 2025

...Great Lakes and Central Appalachians...
Day 1...

Powerful low pressure will continue to produce blizzard conditions
across portions of the Upper Midwest and Great Lakes tonight, but
this system will gradually weaken through D1. The weakening of this
system will be in response to the opening of the upper closed this
evening, becoming negatively tilted as it shifts northeast into
Ontario. At the same time a secondary shortwave trough embedded
within the longwave cyclonic flow across the east will pivot into
the Mid-Atlantic states, and the interaction of these features will
push the primary surface low into Canada will driving a post-
frontal trough across the Appalachians. The overall weakening of
ascent and reduction in moisture will cause precipitation coverage
to fade and become more showery/snow-showery in nature, with the
primarily exception occurring across the U.P. of MI early D1, and
then across the Central Appalachians where pronounced upslope flow
will enhance snowfall Thursday afternoon. WPC probabilities for 4+
inches across these areas are generally 30-50%.


...California, Great Basin, Southwest, and Central Rockies...
Days 1-3...

A closed mid-level low dropping along the Pacific Coast Thursday
will amplify into a full-latitude trough centered across the Great
Basin Thursday night. This will manifest as height anomalies that
are progged via NAEFS to reach as low as -3 sigma with respect to
500-700mb heights late D1, with these anomalies persisting as the
trough slowly moves east with time into the weekend. As the core of
this mid-level low moves across the Four Corners, a downstream
subtropical jet streak will amplify, reaching 150+ kts as it
surges into the Southern Plains. This will place favorable LFQ
diffluence over the Four Corners and into the Central Rockies,
enhancing deep layer lift over the region.

Beneath this upper low, two distinct surface cyclones will also
move across the West. The first will be directly beneath the upper
low moving across the Great Basin and into the Central Rockies D1,
which will tap into increasing PW to expand precipitation across a
large portion of the area. The accompanying air mass if full of
Pacific air, so snow levels will be generally modest, around
4000-6000 ft, but will fall behind the low and accompanying cold
front to 2000-3000 ft. However, this also occurs with decreasing
precipitation coverage and intensity. While coverage of snow is
likely to be widespread D1, the heaviest is expected across
northern UT and into WY where the accompanying warm front will
result in enhanced fgen to drive stronger mesoscale ascent and more
prolonged snowfall rates of 1+"/hr. In this area, WPC probabilities
are high (>70%) for more than 12 inches on D1 across the terrain of
eastern NV, into the Wasatch, Uintas, and Wind Rivers, with
widespread high probabilities (>70%) for 4 inches across much of
NV, eastern ID, and WY. Additionally on D1, WPC probabilities are
high for 6+ inches of snow across the Sierra, and the Transverse
and Peninsular Ranges of CA. By D2, heavy snowfall persists across
the higher terrain of UT and WY while expanding into the CO
Rockies, where WPC probabilities for 6+ inches of additional snow
reach 70-90%.

SW of this secondary low, the pivoting upper low moving across the
Four Corners will drive another area of pronounced ascent leading
to periods of moderate to heavy snow across the Desert Southwest
and extending into the TX/OK Panhandles. The column across this
region is modestly cold enough to support snow, with snow levels
around 5000-6000 ft, but steep lapse rates aloft beneath the cold
core low will help cause strong omega to dynamically cool the
column. This suggests a mixture of rain and snow, possibly becoming
all snow near the surface at times of heavier precipitation rates.
At this time, WPC probabilities D1 are moderate (50-70%) for 6+
inches of snow across the Mogollon Rim, and moderate to high D3
(50-90%) in the Sangre de Cristos. Light snow may expand as far
east as the Panhandle of TX D3 as well.


...Central Rockies into the Central Plains...
Days 2-3...


Secondary lee cyclogenesis will occur east of the Rockies (beneath the aforementioned overlap of jet diffluence and height falls) D2,
leading to a rapidly deepening surface low pressure that will race
eastward in response to confluent/fast flow across the middle of
the country. The parent upper low will weaken with time as it
becomes embedded within this downstream confluent 500mb pattern,
causing the associated vorticity lobe to string out to the east.
Despite this weakening evolution, robust WAA and isentropic ascent,
especially along the 290-295K surfaces, will draw moisture
northward leading to enhanced precipitation shield. The guidance is
in good agreement that a swath of heavy snow, driven primarily by
the overlap of the LFQ of an upper jet streak and low-level
increasing frontogenesis, will drive a translating band of heavy
snow from eastern WY through Iowa D2 into D3. The most intense
fgen will drive ascent into a deepening DGZ (SREF probabilities for
50mb of DGZ depth above 70%) which will support a stripe of heavy
snowfall rates nearing 1"/hr. Although there remains some
latitudinal uncertainty into where this will track, current WPC
probabilities are high (>70%) for 4+ inches D2 from the Pine Ridge
eastward through much of northern NE, with low probabilities
(10-30%) extending into IA D3.


Weiss


$$

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FOUS11 KWBC 060901
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
401 AM EST Thu Mar 6 2025

Valid 12Z Thu Mar 06 2025 - 12Z Sun Mar 09 2025

...Great Lakes and Maine...
Days 1-2...

Primary surface low near the northern Ontario/Quebec border will
continue to drift northeast through today. The negatively tilted
upper trough south of this low will shift up the Mid-Atlantic coast
today with rapid surface cyclogenesis tonight over the Gulf of
Maine. LES on northeasterly flow develops tonight over the eastern
U.P. and over Upstate NY (particularly near Syracuse) where Day
1.5 snow probs for >4" are 40-60%. Wrap around snow lifts over
eastern/northern Maine late tonight/Friday morning with Day 1.5
snow probs for >4" are 40-60% over northern Maine.


...Southwest, Central Rockies across the Central Plains into the
Midwest, then Southern Rockies, and Southern Plains...
Days 1-2...

...Heavy snow bands today into Friday from Wyoming across northern
Nebraska into northern Iowa...

Mid-level low along the far northern CA coast will shift south to
southern CA through tonight before further developing over the Four
Corners Friday night and shifting east to the TX Panhandle Saturday.
Meanwhile, the leading base of the trough currently over SoCal
will eject northeast over the southern Rockies by this afternoon,
across the central Plains tonight before weakening as it approaches
Chicago Friday.

Strengthening SWly jet ahead of the leading trough will allow for
quick ejection and rapid lee-side cyclogenesis over eastern CO/KS
this afternoon through tonight. Rapid banding of precip north of
this low will spread north over much of WY this morning, then shift
east over northern Neb tonight, persisting, but in a weakened state
over IA Friday. Snow totals have increased through this swath with
Day 1 snow probs for >8" over 80% in central WY terrain and 40-70%
over northern Neb. Ample Pacific moisture ahead of this wave will
keep snow levels over the Great Basin and Four Corners 4000-7000 ft
today, but will fall under the upper trough to 3000-4000ft. Day 1
WPC probabilities are high (>70%) for >8" across the terrain of
eastern NV, the Wasatch, Uintas, Wind Rivers, western CO ranges and
the highest terrain along the Mogollon Rim. Day 1 snow probs are
also high for >6" in the SoCal peninsular ranges.

SW of this secondary low, the pivoting upper low moving across the
Four Corners will drive another area of pronounced ascent leading
to periods of moderate to heavy snow across the Desert Southwest
and extending east through the TX/OK Panhandles. The column across
this region is modestly cold enough to support snow, with snow
levels around 5000-7000 ft, but steep lapse rates aloft beneath
the low will help cause strong lift to dynamically cool the
column. This suggests a mixture of rain and snow, becoming all snow
near the surface at times of heavier precipitation rates and in
terrain. Day 2.5 WPC for >6" are 40-80% over the southern Sangre
De Cristos with >4" probs 20-60% east of terrain such as the Raton
Mesa.


Jackson



$$

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FOUS11 KWBC 061859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Thu Mar 6 2025

Valid 00Z Fri Mar 07 2025 - 00Z Mon Mar 10 2025

...Great Lakes and Maine...
Day 1...

Negatively tilted longwave trough extending between two pronounced
shortwaves will pivot northeast across New England and the
Mid-Atlantic tonight. This trough is the remnant of the closed low
which produced a powerful blizzard over the Upper Midwest, and the
southern impulse will likely cause secondary cyclogenesis with
rapid strengthening off of New England and into the Gulf of Maine
tonight. As this low lifts into the Canadian Maritimes, it will
spread heavy snow across Maine, with upstream resultant NW flow
from the Great Lakes into New England driving a combination of lake
effect snow (LES) and upslope snow into the Adirondacks and
Greens/Whites. The heaviest snow is likely across portions of
northeast Maine where WPC probabilities reach 50-70% for 4+ inches
and 30% for 6+ inches. Moderate to heavy snow is also likely across
the eastern U.P., southeast of lake Ontario, and into the
Greens/Whites where WPC probabilities for 4+ inches are as high as
50%.


...Central Rockies through the Upper Midwest...
Days 1-2...

Lee cyclogenesis east of the Rockies will develop this evening
downstream of a positively tilted but amplified upper level trough
swinging through the Great Basin and towards the Central Rockies.
An intensifying and meridionally shifting jet streak downstream of
the primary trough axis will place favorable LFQ diffluence across
the High Plains, additionally supporting the rapid development of
this cyclone. As the low strengthens, it will move almost due east
in response to confluent and increasingly zonal flow across the
central/eastern parts of the CONUS.

As this low pivots east from Colorado to Illinois by Friday night,
it will drive a swath of heavy precipitation to its north, caused
by an overlap of synoptic ascent through the left-exit of the jet
streak aloft, and expanding 850-600mb frontogenesis. At the same
time, moist isentropic ascent, especially in the 290-295K layer
will surge northward creating PWs that will rise to above the 90th
percentile within the CFSR climatology, upon which the ample ascent
will drive a stripe of heavy snow. The warm/moist advection
lifting northward and being acted upon by intense fgen will result
in translating bands of heavy snow. Neutral static-stability
reflected by theta-e lapse rates nearing 0C/km within the axis of
strongest ascent could cause snowfall rates to reach 1+"/hr at
times, which is additionally supported by the WPC prototype
snowband tool, especially from eastern WY through NE. Where these
bands linger, heavy snowfall exceeding 6 inches is likely (>70%)
according to WPC probabilities across eastern WY and NE, with
moderate probabilities (30%) for 4+ inches extending as far east as
central IA.


...Four Corners States...
Days 1-2...

The forecast period begins with an amplified longwave trough
positioned across the Great Basin and extending into the Northern
Rockies. This trough will gradually pivot eastward through D1 and
into D2 as two distinct shortwaves drop from the interior Northwest
through the trough axis and then eject eastward into the Southern
Rockies, eventually merging into a closed low over New Mexico on
Saturday. Impressive height anomalies falling to below the 10th
percentile according to NAEFS ensemble tables over the Southwest
will combine with an increasingly meridionally shaped downstream
jet streak to provide ample ascent across the Four Corners into
Saturday.

At the same time, a surface low will move along the CA coast
beneath this trough evolution and then shift onshore into AZ and
then NM, producing additional ascent to support widespread
precipitation. Snow levels throughout the region will generally
hover in the 4000-5000 ft range, but downstream of the low and
within the most robust warm advection, they may at times rise to as
high as 7000 ft, especially in the Sangre de Cristos D1 into D2
before crashing later Saturday. WPC probabilities D1 for more than
6 inches of snow are high (>70%) in the Ruby Mountains of NV, along
the Wasatch, into the Uintas, CO Rockies, San Juans, and along the
Mogollon Rim. During D2, the highest probabilities become confined
to the Sangre de Cristos and along the Raton Mesa where locally as
much as 12 inches of snow is possible.


Weiss



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FOUS11 KWBC 070855
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 AM EST Fri Mar 7 2025

Valid 12Z Fri Mar 07 2025 - 12Z Mon Mar 10 2025

...New York/New England...
Days 1-3...

Negatively tilted longwave trough over New England will lift north
over the Canadian Maritimes today as the surface low continues to
develop on its transit of the Gulf of St. Lawrence. Heavy snow on
the back side of this surface low under the upper trough will
continue over eastern/northern Maine this morning where Day 1 PWPF
for >6" is 50-80%.

WNW flow off Lake Ontario will continue to allow lake effect snow
(LES) over Upstate NY today with upslope snow over the Adirondacks,
northern Greens, and Whites. Day 1 PWPF for >4" are 20-40% over the
southern Tug Hill down through Syracuse and Utica as well as over
the Presidential Range in NH (which are repeated for Day 2 on
continued upslope flow).

A northern Alberta Clipper tracks over Ontario on Sunday, reaching
northern NY/New England Sunday night. Day 3 PWPF for >4" is around
20% for the northwest facing Adirondacks.


...Central Plains through the Midwest to the North-Central
Appalachians...
Day 1...

The leading shortwave trough from Low pressure over the West is now
over northeast CO and will eject east through the Midwest today on
a strengthening WSWly jet. Robust, but narrow banding continues
across northern Neb/IA early this morning, and shifts east over
Chicago this afternoon. However, the wave is being sheared and the
surface low is filling, so the banding intensity should continue to
wane as it tracks east. Sufficient overlap of synoptic ascent
through the left-exit of the jet streak aloft, 850-600mb
frontogenesis, and ample Gulf-sourced moisture will continue to
drive the snow bands that should see rates drop to moderate by
mid-morning. PWPF for additional snow >2" after 12Z are 30-60% from
northeast Neb across north-central IA and along the IL/WI border.
Snow tonight reaches western PA and the central Appalachians where
there are 20-40% PWPF for >2".


...Four Corners States through Oklahoma/Texas Panhandles...
Days 1-2...

A closed low over over the southern CA border is at the base of the
still positively-tilted trough over the West. This low tracks over
southern AZ today and NM tonight before moving over the TX
Panhandle on Saturday. Further reinforcing troughs will slow the
progress east and prolong the snow fall over AZ terrain today and
the southern Rockies onto the southern High Plains tonight into
Saturday. Snow levels hover in the 4000-5000 ft range over the
Southwest, but start around 6000ft this evening over the I-25
corridor near the CO/NM border/Raton Mesa. Day 1 PWPF for >8" are
50-90% along the Mogollon Rim/White Mtns, and over the southern San Juans/Sangre de Cristos including the Raton Mesa.

Decent dynamics make for snow levels around 3500ft in the TX
Panhandle in banding on the north side of the sfc low. Snow
probabilities have risen here with Day 1.5 PWPF for >4" 40-70%
over the TX/OK Panhandles and over 80% in northeast NM.


...Western Washington...
Days 2-3...

A hearty plume of Pacific moisture tracks into western WA ahead of
the next low dropping south from the Gulf of Alaska Saturday
through Sunday night. Snow levels are generally around 4000ft
through Sunday in the WA Cascades before dropping to 2000ft Sunday
night under the trough axis. Day 2.5 PWPF for >6" is limited to the
highest Olympics/northern WA Cascades, but the Day 3 drops down to
pass level with greater coverage of >40% probabilities.


Jackson



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FOUS11 KWBC 071855
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
155 PM EST Fri Mar 7 2025

Valid 00Z Sat Mar 08 2025 - 00Z Tue Mar 11 2025

...New England...
Day 1...

Sharp cyclonic flow will persist across New England Friday night
and Saturday as an upper low spins across eastern Canada. Within
this flow, a shortwave is progged to drop southeast across New
England Friday night, pushing a surface trough eastward which will
additionally enhance the low-level NW flow. The result of this
evolution will be increased upslope ascent into the Greens and
Whites, leading to rounds of moderate snowfall through D1. The
coverage of snowfall is likely to be modest and confined to the
highest elevations, but WPC probabilities indicate a 50-70% chance
for 4+ inches of snow in northern VT and near the Presidential
Range of NH before precip winds down before D2.


...Four Corners States through Oklahoma/Texas Panhandles...
Day 1...

Strong closed mid-level low characterized by 500mb heights falling
below the 2.5 percentile of the CFSR database will move eastward
slowly across AZ/NM tonight, before slowly beginning to fill over
the TX/OK Panhandles Saturday. Downstream of this closed low, an
upper jet streak will amplify across the Southern Plains, reaching
150 kts while emerging meridionally from near Baja. Together, these
features will produce strong deep layer ascent into the Southern
Rockies. At the same time, moisture being advected into the column
will be impressive as both low-level moisture through S/SE flow
into the system, and upper level moisture on SW isentropic ascent
combine across the region, angling elevated PWs into the southern
High Plains.

The overlap of this deep layer lift and increasing moisture will
result in an axis of moderate to heavy precipitation across NM and
into the OK/TX Panhandles, with low-level easterly flow on Saturday contributing enhanced upslope ascent into the Sangre de Cristos and
along the Raton Mesa. In general, snow levels will be 5000-6000 ft,
but will crash through D1 to as low as 4000 ft before precip wanes
by early D2, but before this occurs heavy snow is likely across the
White Mountains of AZ and especially into the Sangre de Cristos and
along the Raton Mesa where WPC probabilities are high (>70%) for
12+ inches of snow.

Farther east into the Panhandles of TX/OK, the column is marginally
conducive for wintry precipitation. However, strong ascent through
both synoptic and mesoscale forcing could cause periods of dynamic
cooling sufficient to bring snow to the surface. This is most
likely across the TX Panhandle as reflected by HREF 1"/hr snow rate probabilities. The most likely timing for this heavy snow is during
the afternoon hours which will also limit accumulations, but where
dynamic cooling is strong enough and snow can persist, some locally
moderate snowfall accumulations of 2-4" are possible (30-50%
chance).


...Pacific and Interior Northwest...
Days 2-3...

A deepening trough over the Pacific will interact with a building
ridge across the Desert Southwest to funnel strengthening S/SW flow
into the Pacific Northwest beginning Sunday. This will begin to
advect higher moisture onshore as IVT pushes above 250 kg/m/s
according to GEFS and ECENS probabilities. Into this moistening
column, despite the primary trough cutting off and remaining over
the Pacific, a weak shortwave and accompanying vorticity lobe will
swing onshore Sunday evening, and work together with the RRQ of a
jet streak over Canada to induce lift. This will result in
increasing wintry precipitation over the WA Cascades and Olympics,
pivoting into the Northern Rockies by the end of the forecast
period. Snow levels will generally be around 4000 ft during the
heaviest precipitation, but will crash to as low as 1500 ft just
before precip ends Monday aftn. This combined with the transient
nature of forcing suggests most of the impactful snow will remain
above pass levels, but WPC probabilities during D3 rise to as high
as 70-90% for 4+ inches in the WA Cascades, Olympics, and near
Glacier NP.



Weiss



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FOUS11 KWBC 080840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Sat Mar 8 2025

Valid 12Z Sat Mar 08 2025 - 12Z Tue Mar 11 2025


...Southern Rockies through Oklahoma/Texas Panhandles into western
Oklahoma...
Day 1...

Closed low over AZ/NM border will slowly fill as it shifts east to
northwest TX today and along the Red River tonight. A strong SWly
jet streak persists over west TX today, aiding ascent as the
associated surface trough shifts east. This deep layer lift and
increasing moisture will result in expanding precip over N Texas
and OK through this afternoon with an axis of moderate to heavy
precipitation across the TX Panhandle through central OK. Height
falls under the upper low and dynamic cooling in the banding should
allow snow to fall/accumulate over the TX Panhandle into western
OK this afternoon. 00Z HREF mean snow rates are generally not that
high, up to 0.75"/hr, though diurnal effects are probably causing
some of the limitation. Generally speaking, if snow bands become
strong/heavy enough they can overcome diurnal effects and
accumulate. Day 1 PWPF for >4" is 40-60% across the central TX
Panhandle, particularly along the I-40 corridor. Some probabilities
for >2" extend east into OK, but really it comes down to the
banding. The NAMnest likely remains too heavy/snowy, but the recent
HRRRs have trended a bit colder/snowier and a blend of these two
models is probably a decent approach.


...Washington to northwest Montana...
Days 2-3...

A deepening trough from low pressure over the Gulf of Alaska will
interact with a building ridge across the Desert Southwest to
funnel strengthening S/SW flow into western WA tonight, expanding
east to the northern Rockies through Monday. A weak shortwave and
accompanying vorticity lobe will swing onshore Sunday evening, and
along with the right entrance of a jet streak over Canada, enhance
lift. This will result in increasing wintry precipitation over the
WA Cascades and Olympics, pivoting into the Northern Rockies Sunday
night. Snow levels on the WA Cascades will generally be around
4000 ft during the heaviest precipitation, but will crash to as low
as 1500 ft just before precip ends Monday morning. This combined
with the transient nature of forcing suggests most of the impactful
snow will remain above pass levels, but Day 2 WPC probabilities
for >6" are 70-90% in the WA Cascades, with Day 2.5 probs 30-60%
for the Lewis Range in Glacier NP.


The probability of significant icing is less than 10 percent.


Jackson


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FOUS11 KWBC 081817
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
117 PM EST Sat Mar 8 2025

Valid 00Z Sun Mar 09 2025 - 00Z Wed Mar 12 2025


...Pacific Northwest through the Northern Rockies...
Days 1-2...

A deepening trough off the Pacific Coast will amplify into a closed
low positioned west of CA by Monday, while a vorticity streamer cut
off from this feature sheds eastward into the Pacific Northwest.
Downstream of this energy, intensifying SW flow between this trough
and a expanding ridge centered over the Four Corners will drive
modest IVT exceeding 250 kg/m/s into the Pacific Northwest. The
intensifying ascent through WAA, height falls, and diffluence from
the departing RRQ of an upper jet streak into this moistening
column will result in expanding precipitation, first in the
Olympics late D1 and then spreading eastward through the Cascades
and into the Northern Rockies by late D2 before ending quickly. The
transitive nature of the ascent combined with modest available
moisture will limit total precipitation, but heavy snow
accumulations are still likely above 4000-5000 ft. WPC
probabilities D1 are above 70% for 6+ inches, but only across the
Olympics and far northern WA Cascades. Heavy snow expands and
spreads east during D2, reflected by a high risk (>70%) for 6+
inches in the WA Cascades, with a moderate risk (30-50%) across the
Lewis Range in the Northern Rockies.


The probability of significant icing is less than 10 percent.


Weiss



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FOUS11 KWBC 090846
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
446 AM EDT Sun Mar 9 2025

Valid 12Z Sun Mar 09 2025 - 12Z Wed Mar 12 2025


...Upstate New York and Northern New England...
Day 1...

A clipper currently crossing into Ontario will track across
northern New England late tonight. Some Great Lake moisture will be
present in the otherwise continental airmass. Upslope flow onto the
Adirondacks and northern Greens/Whites will lead to snow tonight
with potential for 0.5"/hr snow rates per the 00Z HREF. Given a
weaker clipper will cross this morning, snow from both has Day 1
PWPF for >6" of 30-70% in the highest terrain.


...Washington State to Northwest Montana...
Day 1...

Northern stream shortwave trough crosses WA this evening and
northern MT late tonight. The transitive nature of the trough
combined with modest available moisture will limit total
precipitation, but heavy snow accumulations are still likely above
4000-5000 ft. Day 1 WPC snow probabilities are above 70% for 6+
inches in the higher northern WA Cascades, generally above pass
level, and 30-60% in the higher ridges around Glacier NP. Precip
from this trough quickly cuts off Monday morning across the
Northwest.


...Northwest and California...
Day 3...

A much stronger trough amplifies as it digs off the West Coast
Tuesday night. Enhanced moisture and height falls from the
approaching trough allow moderate precip to cross the PacNW coast
Tuesday night. Snow levels at onset will be near 3500ft in WA,
4500ft in OR, and 5000ft in CA, dropping thereafter through
Wednesday ahead of the trough axis. Particularly heavy snow is
expected in California in noted by Key Messages found on the wpc
website. Further information can also be found in the medium range
discussion (PMDEPD) and from local WFO products.



The probability of significant icing is less than 10 percent.


Jackson



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FOUS11 KWBC 091929
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Sun Mar 9 2025

Valid 00Z Mon Mar 10 2025 - 00Z Thu Mar 13 2025


...Upstate New York and Northern New England...=20
Day 1...

A fast moving clipper-type low will race southeast across Ontario
tonight and move offshore New England Monday morning. Forcing
associated with this clipper will be enhanced downstream due to
height falls/weak PVA ahead of the accompanying shortwave and
modest upper diffluence in the LFQ of a jet streak pivoting across
Canada. Overall, ascent is transient and modest, and available
moisture is just slightly above climo according to NAEFS, so
precipitation is not expected to be heavy. However, where ascent
maximizes, especially into the higher terrain of the upslope
regions of the Adirondacks, Greens, and Whites, snowfall rates of
0.5" to 1" per hour are likely at times. This will result in local
snowfall exceeding 4" as reflected by WPC probabilities that are as
high as 30-50% in these areas.


...Washington State to Northwest Montana...=20
Day 1...

Fast moving shortwave trough of modest amplitude will shed from an
amplifying longwave trough over the Pacific and race across the
Northwest tonight through Monday. Height falls associated with this
impulse will drive synoptic lift, while a subtle period of WAA on
backing mid-level flow to more S/SW enhances moisture on IVT which
is progged by NAEFS to briefly pulse above the 97th climatological
percentile. Jet-level support is modest, but sufficient deep layer
lift into the moistening column will result in periods of moderate
to heavy snow, especially in the Cascades and Northern Rockies
where low to mid level westerly flow drives additional upslope
enhancement. Snow levels above 4000-5000 ft will confine heavy
accumulations to only the highest passes and higher elevations, but
in these regions WPC probabilities for 6+ inches are as high as
70-90%.


...Pacific Coast...=20
Day 3...

A much stronger trough than the one from D1 above amplifies off the
Pacific Coast beginning Tuesday, driving an expansive area of
height anomalies between 700-500mb that fall to below the 2.5
climatological percentile according to NAEFS by 00Z/Thursday. While
these height falls are progged to remain just west of the coast by
the end of the forecast period, the resultant downstream shift to
S/SW flow onshore CA and the Pacific Coast will surge IVT onshore
as an atmospheric river (AR). Recent IVT probabilities from both
the GEFS and ECENS have increased, and although the GEFS remains
more amplified (40% IVT exceeding 500 kg/m/s), the ECENS has a few
members that feature IVT exceeding 750 kg/m/s. Regardless of the
maximum IVT, it is likely that heavy precipitation will spread
onshore, with elevated instability due to deep lapse rates
exceeding moist adiabatic levels as the trough advects east. This
suggests that despite general short duration of the highest IVT,
precipitation coverage and intensity will be significant.

Within the WAA which demarcates the onset of the AR, snow levels
will climb to around 3000 ft over WA state, and as high as
5000-6000 ft in CA according to the NBM deterministic forecasts.=20
As the accompanying surface low and attendant upper trough swing=20
towards the coast late (and more into D4), snow levels will drop=20
rapidly, becoming more impactful to many western passes. At this=20
time, through D3, the heaviest snow accumulations are expected=20
across the northern Sierra and Shasta/Trinity region of CA where=20
WPC probabilities feature a high risk (>70%) for 8+ inches and=20
locally 1-2 feet is possible. Farther north into the Cascades of WA
and OR, as well as the Olympics, lighter snows have a moderate=20
chance (30-50%) of exceeding 6 inches, but with snow levels around=20
3000 ft more area passes will experience impactful snow.

This system will likely become significant across much of the West
into the medium range, and Key Messages, linked below, have been
issued for this event.


The probability of significant icing is less than 10 percent.=20


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8KPdSJ-mo2IcmjWkJDJ1tS4OyVRV-4twy5qGpfX5gRsKo= J3Quf8iulZTABuqctFNYZq_m-fd1yLonMB_MnXkktl-SYU$=20

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FOUS11 KWBC 100848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
448 AM EDT Mon Mar 10 2025

Valid 12Z Mon Mar 10 2025 - 12Z Thu Mar 13 2025


...The Bitterroots...=20
Day 1...

A plume of Pacific moisture continues to push northeast from
northern OR through western MT this morning as a quick-moving=20
northern stream shortwave trough of modest amplitude shifts east
over the northern Rockies. Moderate snow rates can be expected
above the roughly 4000ft snow levels in this plume that will be
focused on the Bitterroots along the ID/MT border this morning. Day
1 PWPF for >6" additional snow after 12Z is 30-60% along the
Bitterroots and toward the western slopes around Glacier NP.


...Pacific Coast...=20
Days 2/3...

...Impactful heavy snow for California terrain Wednesday and
Thursday. See Key Messages linked below...

A powerful and deep trough digs off the West Coast Tuesday night
before shifting onshore Wednesday night through Thursday. The=20
orientation of this trough, with its base digging south from the=20
Central CA to Southern CA coasts Thursday brings a fairly short
lived surge of Pacific moisture that when combined with upslope
flow and height falls from the approaching trough brings a potent
heavy snow event for the length of California. This heavy snow
begins in the Klamath and CA Cascades late Tuesday night and the
length of the Cascades Wednesday into Thursday and SoCal ranges
Thursday. Snow levels of 4000 to 5000ft can be expected during the
heaviest snow for all California terrain. Day 3 PWPF for >18" is
60-90% for the highest Klamath/CA Cascades and 70-100% for the
length of the Sierra Nevada.

Lighter precip rates are expected over WA/OR which will be well
north of the base of the trough. Snow levels on Wednesday are close
to 3000ft in WA and 4000ft in OR. Day 3 PWPF for >6" are 50-70% in
the WA/OR Cascades as well as the Sawtooths of ID.

Snow and wind will spread across the Intermountain West and Rockies
Thursday into Friday before rapid development occurs over the
Plains as noted in the Key Messages and the medium range discussion
(PMDEPD).


The probability of significant icing is less than 10 percent.=20


Jackson




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!6bl38HPUTWxgEiSI7mRxEPXjaMbgnGedZ19lAV5k_3qEs= zA4oslTxCmo2WQjkaOMBTCzeJpSt97EfgY50x2UcFFsD4E$=20

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FOUS11 KWBC 101902
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Mon Mar 10 2025

Valid 00Z Tue Mar 11 2025 - 00Z Fri Mar 14 2025


...The West...
Days 2-3...

...Impactful heavy snow from the California mountain ranges=20
Wednesday to the Intermoutnain West late week. Please see current=20
Key Messages below...

An upper-level trough in the northeast Pacific will direct an
atmospheric river at California starting Tuesday night and
continuing through Wednesday. Mountain snow begins Tuesday night from
the Cascade Range on south to the Siskiyou/Shasta and northern=20
Sierra Nevada. By 18Z Wednesday, ECMWF SATs shows a SWrly >400=20
kg/m/s IVT that surpasses the 97.5 climatological percentile over=20
central California. This enhanced moisture transport combined with=20
a cold frontal passage and falling heights aloft will result if=20
plummeting snow levels Wednesday night along the Sierra Nevada=20
with heavy snow as low as 5,000ft in elevation. Hourly snowfall=20
rates between 2-3"/hr are expected in these ranges, with the=20
combination of heavy/wet snow also posing a potential risk for=20
scattered areas of power outages and tree damage. Snow will also=20
unfold into the Southern California ranges north and east of Los=20
Angeles and San Diego Wednesday night and into Thursday morning.=20
Minor snow accumulations are possible as low as 4,000ft in the San=20
Rafael, San Gabriel, and San Bernadino Mountains through the day on
Thursday. WPC probabilities between 00Z Wed - 00Z Fri show high=20
chances (>70%) for snowfall totals >24" along the entire length of=20
the Sierra Nevada above 6,000ft. Some areas above 8,000ft could see
as much as 4-5 feet of snowfall by the time a break in the snow=20
arrives Thursday night. The WSSI is depicting Major to Extreme=20
Impacts in the Sierra Nevada that is driven due to the Snow Amount=20 algorithm, as well as some inclusion of the Snow Load and Blowing=20
Snow elements as well. Note that the Cascades above 4,000ft and=20
Olympics above 3,000ft have high chances (>70%) for snowfall=20
accumulations >6" through Thursday afternoon.

East of the Pacific Mountain ranges, the expansive swath of
Pacific moisture will expand well inland Wednesday night and into
the second half of the week. The heaviest snowfall is likely to
occur on Thursday as the cold front sweeps across the Intermountain
West and the diffluent left-exit region of a 250mb jet streak
positions itself overhead. Snow is likely to continue a little
longer into Tuesday night and Friday, so for more on those=20
potential snowfall details, please refer to our medium range=20
discussion. WPC probabilities through 00Z Friday depict high=20
chances (>70%) for snowfall >8" in parts of the Blue, Sawtooth,=20
central and southern Nevada terrain, portions of the Wasatch, and=20
the tallest peaks of the Mogollon Rim.=20

Mullinax

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-IQTm_3w1FygAcymNlQ8IwRhPbTWgNwRlD0GP28prHj5D= LW3yx0e3hNGkWQs-DmBFznU6h7fL2c4WS__FPaaMfFDaVA$=20

$$

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FOUS11 KWBC 110849
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Tue Mar 11 2025

Valid 12Z Tue Mar 11 2025 - 12Z Fri Mar 14 2025


...The West...
Days 1-3...

...Impactful heavy snow for most California mountain ranges=20
Wednesday into Thursday, then mostly the southern Intermountain=20
West and Rockies late week. Please see current Key Messages linked=20
below...

A strong northern stream trough currently rounding a cold-core low
over the Gulf of Alaska will further strengthen as it dives south
off the West Coast through Wednesday. The base of the trough
continues to dig south from the Central to Southern California
Coasts Thursday before ejecting east over the Four Corners Thursday
night and re-developing into a deep low over the south-central=20
Plains Friday.=20

Mountain snow begins tonight as moisture streams in ahead of the
trough axis along the length of the Cascade Range through the=20 Siskiyou/Shasta and northern Sierra Nevada. Day 1 snow
probabilities for >6" are 30-70% in the WA Cascades which will
expand and increase for Day 2 as snow rates increase to moderate=20
and snow levels drop below many Cascades passes.

This moisture surge shifts inland over CA Wednesday through=20
Wednesday night with the now heavy precipitation axis shifting=20
south with the base of the trough with snow levels generally 5000=20
to 6000ft at the onset of heavy snow. Height falls from the=20
approaching trough axis allow snow levels to drop Wednesday=20
afternoon through night along the Sierra Nevada with heavy snow as=20
low as 4,500ft in elevation before rates decrease (as low levels=20
further drop). The cooling column and ample moisture should result=20
in extreme hourly snowfall rates of 2-4"/hr in these ranges. The=20
combination of heavy/wet snow and increasing winds also posing a=20
potential risk for scattered areas of power outages and tree=20
damage. Day 2 snow probabilities for >18" are 50-99% in the=20
Shasta/Siskiyou and along the length of the higher Sierra Nevada.=20
1 to 4ft can generally be expected above about 6000ft.

Heavy snow will also reach the Transverse Ranges in Southern=20
California Wednesday night through Thursday morning with snow
levels dropping from around 6000 to 4000ft. Day 2.5 WPC snow
probabilities are 50-90% for the higher San Gabriel and San
Bernardino Ranges. 00Z Wed

East of the Pacific Mountain ranges, the expansive swath of
Pacific moisture will expand well inland Wednesday night through
Thursday night. The heaviest inland snowfall is likely to occur on
Thursday as the powerful cold front sweeps across Nevada, Utah, and
northern Arizona before shifting across Colorado and New Mexico=20
Thursday night. Day 3 snow probabilities for >8" are 40-80% over
the central and southern NV ranges, much of Utah terrain, the=20
Kaibab Plateau north of the Grand Canyon, along the Mogollon Rim to
the White Mtns of AZ, and the San Juans of southwest CO. This low
rapidly re-develops Friday over the south-central Plains.=20

The next wave quickly shifts toward the OR/CA border Thursday night
on a powerful NWly jet. Further info on the redeveloping low over
the Plains and the next wave into the West Coast can be found in
the WPC medium range discussion (PMDEPD), and from local WFOs.


The probability of significant icing is less than 10 percent.

Jackson


...Winter Storm Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!772UHlvrtnBNkfIjPO3UqHE03jBZmrTEFUbYxmudJYhU5= Ahm4ZbiK5vPtQFAeXiMkcbZ_h6sPJfqxyXAgWLn2bfA3Ro$=20

$$

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FOUS11 KWBC 111907
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Tue Mar 11 2025

Valid 12Z Tue Mar 11 2025 - 12Z Fri Mar 14 2025


...The West...
Days 1-3...

...Impactful heavy snow for most California mountain ranges=20
Wednesday into Thursday, then mostly the southern Intermountain=20
West and Rockies late week. Please see current Key Messages linked=20
below...

An upper-level trough in the northeast Pacific will dive south
towards the West Coast and direct an atmospheric river at
California starting Tuesday night and continuing into the second
half of the week. The enhanced moisture transport combined with a
cold frontal passage and falling heights aloft will result in
plummeting snow levels along the Cascade Range on south to the
Shasta/Siskiyou tonight, then along the Sierra Nevada through
Wednesday and into Wednesday night. By 00Z Thursday, a >400 kg/m/s
SWrly IVT (topping out near the 99th climatological percentile via
ECMWF SATs) will be aimed at central California at the same time
the cold front pushes through "The Golden State". This when
snowfall rates will be at their heaviest; Wednesday afternoon into
Wednesday night, along the Sierra Nevada. Snowfall rates of 2-3"/hr
will be common from 6,000ft and up along the Sierra Nevada at the
snow's peak intensity. Farther south, the Transverse Ranges as well
as the peaks of the Peninsula Ranges are likely to see heavy snow
above 5,000ft through Thursday morning. Some upslope flow will=20
linger into the Sierra Nevada Thursday morning, before a brief=20
lull in the action arrives Thursday afternoon. By Friday morning,=20
yet another Pacific storm system arrives, but with notably higher=20
snow levels compared to the Wed-Thurs storm system.=20

Overall, this is an exceptionally snowy pattern for the
Salmon/Siskiyou/Shasta of northern California and along the entire=20
length of the Sierra Nevada. Snowfall will be measured in feet with
as much as 4-5 feet forecast in the peaks of the Sierra Nevada.=20
For elevations above 5,000ft in northern California, above 6,000ft=20
in the central/southern Sierra Nevada, and above 6,000ft in the San
Gabriel and San Bernadino of southern California, snowfall amounts
are likely to range between 1-3 feet of snow. WPC's WSSI shows=20
Major to Extreme Impacts in most of these ranges with Snow Amount=20
the primary impact denoted in the algorithm, but some impacts as a
result of Snow Load and Blowing Snow are expected as well.=20
Dangerous to impossible travel are anticipated with the potential=20
for some instances of power outages and tree damage as well.

The highly anomalous IVT responsible for the barrage of heavy snow
in the California mountain ranges will advect moisture well inland
across much of the Intermountain West as well. Heavy mountain snow
is expected in the more remote areas of the Blue, Sawtooth, and
Absaroka of the northern Rockies. The same recipe that produced
heavy snow in the Sierra Nevada (moisture advection, strong cold
FROPA, upslope flow) will coincide with the added help of strong
diffluent flow downstream of the upper trough to generate heavy=20
snow from the Tetons on south through the Bear River, Wasatch,=20
Uinta, central Nevada ridges, the Mogollon Rim, and Colorado=20
Rockies. WPC probabilities show high chances (>70%) for snowfall=20
totals >8" in all of these mountain ranges, but it is the Wasatch,=20
Uinta, and Mogollon Rim most notably that could see snowfall totals
between 1-2 feet through Friday.


The probability of significant icing is less than 10 percent.


Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_ou8Slwrrxr1jRi9f6xFz5MYD7l8CGNKyR4gSO6EGFnFf= 43foJjm1O1Kl4uKTrtYSAIIjs25nhEgk_9-FQ-4SgLKV00$=20

$$

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FOUS11 KWBC 120907
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
507 AM EDT Wed Mar 12 2025

Valid 12Z Wed Mar 12 2025 - 12Z Sat Mar 15 2025


...The West...
Days 1-3...

...Impactful heavy snow for most California mountain ranges=20
this afternoon into Thursday, mostly the southern Intermountain=20
West terrain and Rockies late week, then blizzard potential on the
northern Plains Saturday. Please see the latest Key Messages=20
linked at the bottom...

Potent upper-level trough continues to dig as it tracks south with
the parent low drifting south from the Gulf of Alaska. The base of
the trough approaches northern CA this afternoon, then digs south
to the northern Baja through Thursday. Enhanced moisture transport
has raised snow levels to around 3500ft in WA, 4500ft in OR,=20
5000ft in northern CA and 6000ft on the Sierra Nevada. However, the
cold frontal passage and falling heights aloft will result in snow
levels generally around 3500ft along the Cascade Range on south to
the Shasta/Siskiyou this evening and 2500ft late tonight as snow=20
rates decrease after the upper trough passage.=20

The Sierra Nevada will be the focus of the moisture plume which
features >400 kg/m/s SWrly IVT (near the 99th climatological=20
percentile via ECMWF SATs) just ahead of the cold frontal passage
this evening. This when snowfall rates will be at their heaviest...=20
2-3"/hr will be common per 00Z HREF for several hours between 20Z=20
and 10Z Thursday down the length of the Sierra Nevada above about=20
6,000ft which is where Day 1 PWPF for >18" snow is categorical. Some
upslope flow will linger into the Sierra Nevada Thursday morning,=20
before a brief lull in the action arrives Thursday afternoon.=20

By Friday morning, the next Pacific storm system arrives, producing
more moderate snow rates for the Cascades and Sierra Nevada.
However, snow levels now progged to remain low through this time,=20
around 1500ft in western WA, and 2500 to 3000ft OR through the
Sierra Nevada. Day 3 PWPF for >8" is 40-80% for the OR Cascades and Shasta/Siskiyou, peaking around 60% for the WA Cascades and Sierra
Nevada.

Farther south, the Transverse Ranges as well as the higher peaks=20
of the Peninsular Ranges will see heavy snow late tonight through=20
Thursday morning as the snow levels drop from 5500ft to 4000ft. Day
2 PWPF for >8" are 40-80% in the higher terrain.


Overall, this is an ideal pattern for somewhat brief, but heavy
snow for the Shasta/Siskiyou and along the entire length of the=20
Sierra Nevada. Snowfall will be measured in feet with as much as=20
4-5 feet forecast in the peaks of the Sierra Nevada and 3 feet at
the higher pass levels such as on I-80. The WSSI retains shows=20
Major to Extreme Impacts in most of these ranges with Snow Amount=20
the primary impact, but some impacts as a result of Snow Load and=20
Blowing Snow are expected as well. Dangerous to impossible travel=20
are anticipated with the potential for some instances of power=20
outages and tree damage as well.

The highly anomalous IVT responsible for the barrage of heavy snow
in the California mountain ranges will advect moisture well inland
across much of the Intermountain West as well. Heavy mountain snow
is expected in the Blue, Sawtooth, and Absaroka of the northern=20
Rockies. The high moisture plume will coincide with the added help
of strong diffluent flow downstream of the upper trough to=20
generate heavy snow from the Tetons on south through the Wasatch,=20
Uinta, central Nevada ridges, the Kaibab Plateau and Mogollon Rim,
and western Colorado Rockies. Day 1.5 and 2 WPC probabilities show
high chances (>70%) for snowfall totals >8" in all of these=20
mountain ranges, but it is the Wasatch, Uinta, and Mogollon Rim=20
most notably that could see snowfall totals between 1-2 feet=20
through Friday.


...Northern Plains...
Day 3...

The trough takes on a negative-tilt Thursday night over NM and
closes in to a mid-level low over KS Friday morning. This low
further deepens/strengthens as it tracks northeast over MN into
Saturday. The southern stream wave crossing the southern Plains=20
today limits Gulf moisture from streaming up the Plains until=20
Thursday night, limiting the the moisture available moreso than if
the wave weren't crossing today. While enough Pacific- sourced=20
will be present to allow some wrap around banding on the low over=20
the High Plains Friday that banding should be fairly sparse until=20
Friday night when the activity should be over central Neb/SD. This
is notable as the area is in drought and will be experiencing
strong winds ahead of the system - in some areas of the High Plains
there may be just a dry wind shift. Once those bands do develop as
they head for the eastern Dakotas and MN, heavy snow banding is
possible. Powerful winds with the system will immediately result in
blowing snow and a potential blizzard. Marginal thermals at the
onset should result in a rain to wintry mix to snow progression
with some ice accretion potential most likely over the Red River of
the North Basin along the ND/MN border.


Jackson



...Winter Storm Key Messages are in effect as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_nmiYIOHPo2OAAoL3oAPwm67D4v9iY77Xadgu2ho1RewG= E3T8xDMOs4bcqJeiY3YhlrHad8jMBEpnm-i_diVoCQcsIE$=20

$$

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FOUS11 KWBC 121919
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 PM EDT Wed Mar 12 2025

Valid 00Z Thu Mar 13 2025 - 00Z Sun Mar 16 2025


...The West...
Days 1-3...

...Storm system to produce impactful heavy snow for most=20
California mountain ranges through Thursday, the southern=20
Intermountain West terrain and Rockies late week, then emerge over=20
the Central U.S. on Saturday with blizzard potential over parts of=20
the northern Plains. Please see the latest Key Messages linked at=20
the bottom...

Potent upper-level trough continues to dig as it tracks south with
the parent low drifting south from the Gulf of Alaska. The base of
the trough and associated cold front approaches northern CA this=20
afternoon, then digs south to the northern Baja while also pushing
inland through Thursday. Enhanced moisture transport has raised=20
snow levels to around 4000ft in WA, 4500ft in OR, 5000ft in=20
northern CA and 6500ft on the Sierra Nevada. However, the cold=20
frontal passage and falling heights aloft will result in snow=20
levels generally around 3500ft along the Cascade Range on south to=20
the Shasta/Siskiyou this evening and 2500ft late tonight as snow=20
rates decrease after the upper trough passage.=20

The Sierra Nevada will be the focus of the moisture plume which
features >400 kg/m/s SWrly IVT (near the 99th climatological=20
percentile via NAEFS SATs) just ahead of the cold frontal passage=20
this evening. This is when snowfall rates will be at their=20
heaviest per the 12z HREF and around 2-3"/hr for several hours=20
between 00Z and 10Z Thursday down the length of the Sierra Nevada=20
above about 6,000ft, which is where Day 1 PWPF for >24" snow is=20
above 80%. Some upslope flow will linger into the Sierra Nevada=20
Thursday morning, before a brief lull in the action arrives=20
Thursday afternoon.=20

By Friday morning, the next quick-hitting Pacific storm system=20
arrives, producing more moderate snow rates for the Cascades and=20
Sierra Nevada. However, snow levels are progged to remain low=20
throughout this time period, around 1500ft in western WA, and 2500
to 3000ft OR through the Sierra Nevada. Eventually, the next=20
progressive shortwave digging across the northern Pacific produces
upstream ridging across the West Coast by Friday night and raises=20
snow levels up to 4000ft across northern CA on Saturday. This sets=20
the stage for the next Atmospheric River event progged to impact=20
northern CA and southern OR primarily on Day 4. For the Day 2-3=20
time frame, PWPF for >8" is 60-90% for the OR Cascades and=20
Shasta/Siskiyou.

Farther south, the Transverse Ranges as well as the higher peaks=20
of the Peninsular Ranges will see heavy snow late tonight through=20
Thursday morning as the snow levels drop from 5500ft to 4000ft. Day
1 PWPF for >8" are 60-90% in the higher terrain.

Overall, this is an ideal pattern for somewhat brief, but heavy
snow for the Shasta/Siskiyou and along the entire length of the=20
Sierra Nevada. Snowfall will be measured in feet with as much as=20
4-5 feet forecast in the peaks of the Sierra Nevada and 3 feet at
the higher pass levels such as on I-80. The WSSI retains Major to=20
Extreme Impacts in most of these ranges with Snow Amount the=20
primary impact, but some impacts as a result of Snow Load and=20
Blowing Snow are expected as well. Dangerous to impossible travel=20
are anticipated with the potential for some instances of power=20
outages and tree damage as well.

The highly anomalous IVT responsible for the barrage of heavy snow
in the California mountain ranges will advect moisture well inland
across much of the Intermountain West as well. Heavy mountain snow
is expected in the Blue, Sawtooth, and Absaroka of the northern=20
Rockies. The high moisture plume will coincide with the added help
of strong diffluent flow downstream of the upper trough to=20
generate heavy snow from the Tetons on south through the Wasatch,=20
Uinta, central Nevada ridges, the Kaibab Plateau and Mogollon Rim,
and western Colorado Rockies. Days 1-2 WPC probabilities show high
chances (>70%) for snowfall totals >8" in all of these mountain=20
ranges, but it is the Wasatch, Uinta, and Mogollon Rim most notably
that could see snowfall totals between 1-2 feet through Friday.


...Northern Plains...
Day 3...

The trough takes on a negative-tilt Thursday night over NM and
closes in to a mid-level low over KS Friday morning. This low
further deepens/strengthens as it tracks northeast over MN into
Saturday. MSLP of this low is expected to drop into the 970s (mb)
and drop below the 1st climatological percentile per the GEFS and
ECENS. This extremely low pressure will be the driving force behind
the widespread strong winds poised to be the primary weather=20
hazard across the northern Plains.

The southern stream wave crossing the southern Plains today limits
Gulf moisture from streaming up the Plains until Thursday night,=20
cutting off the moisture available moreso than if the wave weren't
crossing today. While enough Pacific- sourced will be present to=20
allow some wrap around banding on the low over the High Plains=20
Friday that banding should be fairly sparse until Friday night when
the activity should be over central Neb/SD. This is notable as the
area is in drought and will be experiencing strong winds ahead of=20
the system - in some areas of the High Plains there may be just a=20
dry wind shift. Once those bands do develop as they head for the=20
eastern Dakotas and MN, heavy snow banding is possible. Powerful=20
winds with the system will immediately result in blowing snow and a
potential brief blizzard. Marginal thermals at the onset should=20
result in a rain to wintry mix to snow progression with some ice=20
accretion potential most likely over the Red River of the North=20
Basin along the ND/MN border. This transition occurring during the
overnight period could limit snowfall totals as well. Latest WPC=20 probabilities for at least 4" of snow are medium (40-60%) from the=20
eastern Dakotas through far western and north- central Minnesota.=20
WSSI-P values for moderate impacts are mainly associated with=20
Blowing Snow and are within the 50-70% range for this region.


Snell/Jackson




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5aU9N937f7uNKvw_kUgp6fyzcmNgN7juUKpq3BExQTmus= oI0UywSgFcPSTjy2-LCHxL1MAZ39zTZVOKY7M_axVBY5Jo$=20

$$

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FOUS11 KWBC 130703
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EDT Thu Mar 13 2025

Valid 12Z Thu Mar 13 2025 - 12Z Sun Mar 16 2025


...The West...
Days 1-3...

...Extremely active weather pattern will spread heavy snow across
most of the West today through Friday, with a second wave
approaching for the weekend. This lead system will likely become a
significant winter storm in the Northern Plains Saturday. Key
Messages are in effect, and linked below...


The period begins with a short wavelength but extremely amplified
trough aligned on the immediate Pacific coast Thursday morning.
This trough will continue to amplify as it moves across the Great
Basin Thursday evening and then into the Rockies on Friday. During
this evolution, a potent shortwave and accompanying vorticity
maxima will swing through the base of this trough, This feature
will outrun the northern leg of this trough, resulting in a closed
mid-level low pivoting into the Southern Rockies Friday morning and
then into the Southern Plains. This will be an extremely impressive
feature, as NAEFS ensemble tables indicate 500-700mb heights fall
below the minimum within the CFSR database by Friday morning across
the Central and Southern Rockies, with a surrounding large area of
height anomalies below the 1st percentile across most of the
Western U.S.

This mid-level height evolution is a clear signal for a powerful
and widespread system to bring heavy precipitation across an
expansive area. While height falls will drive ascent across a vast
region, this will combine with upper diffluence within the LFQ of a
subtropical jet streak which will wrap around the base of this
trough, producing enhanced deep layer lift, especially into CA and
the Four Corners. Additionally, periods of upslope flow on W/SW 700
mb winds will enhance ascent across much of the terrain, first
across the Sierra and Cascades, and then spreading east across the
Great Basin and into the Rockies Friday. Additionally, W/SW mid-
level flow will isentropically ascend the region, leading to
additionally enhanced lift across a large portion of the region.

In the presence of this pronounced ascent, moisture will steadily
increase as an atmospheric river (AR) pivots onshore downstream of
the primary trough axis. IVT progs from both the GEFS and ECENS
indicate a high probabilities (>90%) for a plume of 250 kg/m/s=20
IVT, although probabilities for 500 kg/m/s IVT are tepid (< 30%).
Still, this pronounced moisture plume will surge PWs to above the
90th climatological percentile from CA through the Southern
Rockies, with more normal PWs farther north. The overlap of the
aforementioned ascent into this moistening column will result in
widespread precipitation, with snow falling in the terrain.

While confidence is high in widespread precipitation, there is
still uncertainty into the snow levels. The steep lapse rates
beneath the core of the deepening upper trough suggest heavy
precipitation rates will drag down snow levels, indicating lower
NBM percentiles are likely more realistic. Using the NBM 25th
percentile as proxy, snow levels could fall to 2000-3000 ft during
periods of heavy snow across much of the West, with heights as low
as 1000-1500 ft across the Cascades. This indicates that travel
across many passes will be greatly impacted, especially where
snowfall rates reach 1-2"/hr, potentially as high as 3"/hr across
the Sierra, Transverse Ranges of CA, and parts of the Great Basin
terrain as reflected by the WPC prototype snowband tool.

Not only will rates be impressive, they will combine with strong
winds to produce substantial impacts, and the WSSI-P is forecasting
a high probability (>90%) for at least moderate impacts for much of
the terrain, especially from CA through the Four Corners. In these
areas, WPC probabilities forecast a high chance (>90%) for at least
8 inches D1 in the Sierra, Transverse/Peninsular Ranges, the
Wasatch, Mogollon Rim, San Juans, Uintas, and Wind River Mountains.
By D2 lingering snowfall may accumulate above 8 inches once again,
but primarily across the CO Rockies. Locally 1-3 feet of event
total snowfall is probable in these ranges.

As this first impulse departs into the Central Plains D2, /00Z-12Z
Saturday/, another wave immediately on its heels will approach the
Pacific Coast and spread renewed height falls onshore as far east=20
as the Central Rockies. This second wave appears to be less intense
as reflected by weaker height and PW anomalies, and is progged to=20
be shifted north of the initial impulse. However, renewed periods=20
of heavy snowfall are likely from the Sierra and northern CA
terrain north and east into the Cascades and then spread east D3
into the Rockies, generally from CO northward as a warm front
pivots through the area. Snow levels with this second wave are
expected to be higher, rising to 4000-5000 ft in CA and 2500-3500
ft elsewhere, but still low enough to be impactful to many passes
as Pacific air is slow to flood eastward.=20

With this second wave, WPC probabilities D2 re-focus in the=20
Sierra, the Shasta/Trinity region of northern CA, and the OR=20
Cascades where they are above 70% for 8+ inches. On D3 these
probabilities shift northeast, with 70%+ probabilities extending
across the WA/OR Cascades, the Olympics, and into the Salmon River
range.


...Central and Northern Plains...=20
Days 2-3...

The southern stream closed low emerging from the Four Corners and
into the Southern Plains Friday morning will become a formidable
winter storm across the Plains Friday into Saturday. As this closed
low emerges into the Plains early Friday, it will continue to
deepen, featuring 500-700mb height anomalies by 00Z Saturday that
are below the minimum percentile within the CFSR climatology=20
between 850-500mb across a large portion of the Plains. This is an=20 exceptionally deep system, and the combination of the intense=20
height falls with the LFQ of a subtropical jet streak rotating=20
through the trough will result in rapid lee-cyclogenesis beginning=20
as early as Friday morning.=20

This surface low will deepen rapidly, approaching March record
pressure levels across the Plains as it tracks from eastern CO
Friday morning to eastern SD Friday evening, and then the U.P. of
MI Saturday aftn. While there is some uncertainty in the exact
placement and track of this low, the overall spread is relatively
small for a D3 system, leading to high confidence in the evolution.
With this low deepening rapidly, significant moisture will be drawn
northward from the Gulf on impressive isentropic ascent, and the
resultant theta-e ridge is progged to lift into a robust TROWAL
which will pivot across WI and into MN/ND/SD Saturday morning. As
this occurs, the combination of increasing ascent, aided by a
pivoting deformation axis W/NW of the low center, and cooling of
the column through both dynamic affects and ageostrophic flow/cold
air drainage from the NNW, will result in a p-type transition from
rain to mixed to snow.=20

There remains uncertainty into how long this transition will take
to occur, but the intense omega into the column Saturday morning
suggests the guidance may be under-doing the speed at which this
occurs, indicating a faster transition from rain to snow, with less
freezing rain/sleet in between. This is more typical of the
conceptual model for this type of system as well, so while mixed
precip is likely at times, the more impactful wintry precipitation
type should be snow, which will likely come down heavy at times. At
the same time, very strong winds, which are progged by model
soundings to exceed 50 kts in the 800-900mb layer, while help to
fracture dendrites leading to low SLRs which will be blow around
considerably. So, while total snowfall may be somewhat modest
except beneath the pivot point of this deformation axis, impacts
will be substantial with near blizzard conditions possible from far
northeast Nebraska through northern Minnesota. In this area, 48-hr
WPC probabilities from 12Z Fri to 12Z Sunday reach as high as
50-70% for 4+ inches, and isolated totals above 6 inches are
possible (10-30%). Additionally, some light freezing rain has a
30-50% chance of accumulating 0.1" or more in a small portion of NW
MN.



Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4JGcCzvCafQcT1jc4Ei5rPfHvAyePsBmOR_cNx3GMRAww= oQNdiaX0-IumDfDLsxIjjgBE0G5slHNYvL7IcLSB4QYBKM$=20

$$

=3D =3D =3D
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FOUS11 KWBC 131945
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu Mar 13 2025

Valid 00Z Fri Mar 14 2025 - 00Z Mon Mar 17 2025

...The West...
Days 1-3...

...Extremely active weather pattern will spread heavy snow across
most of the West through Friday, with a second wave approaching=20
for the weekend...

A series of potent upper level shortwave troughs will move across=20
the West through this period, resulting in multiple rounds of heavy
snow across much of the terrain from the Cascades, Sierras, the=20
Front Range, and much of the terrain in between. This very active=20
period with multiple rounds of snow and low snow levels could=20
result in impacts to the various mountain passes across the West,=20
with snow accumulations measured in feet.

The first and most potent of the upper level troughs is moving
across the West right now. A vorticity maximum rounding the base of
the trough along the West Coast now will move into the Southwest
tonight. Ahead of this trough, lee cyclogenesis is ongoing across
the northern and central Plains. The combination of this trough and
surface lows will focus the heaviest associated snow from the
Bighorns of MT/WY south through the Front Range and into the
Sacramento Mountains of NM tonight.

Snow levels will be above 7,000 ft across these easternmost ranges
of the Rockies to start the night, but as the trough and associated
cold air moves in tonight, they will drop to generally between
2,000 and 3,000 ft, allowing snow to begin to accumulate to pass
level by the start of the day Friday. As the Plains low
consolidates into one primary low over western Kansas and Nebraska,
the snow should similarly focus across Wyoming, Colorado, and
eastern Utah Friday morning, where the heaviest snow totals are
expected for the Day 1/Thursday Night & Friday period. WPC 24 hour probabilities through Friday afternoon of 6 inches of snow or more
are as high as 80% in southwest Colorado, but are above 50% across
much of western Colorado, the Uintas of Utah, and the eastern=20
Mogollon Rim of central Arizona. The low shifts into the eastern
Plains by Friday afternoon, ending the snow for the Rockies for
this system.

A second upper level shortwave and the leading edge of a potent
northwesterly jet streak will follow behind the first into the=20
West Coast early Friday morning. The rapid succession of the waves
could mean some of Rockies may have only a brief break in the snow, particularly across the Four Corners region, before precipitation
rates increase once again associated with the approach of the
second wave. This shortwave will be weaker than the first, but=20
will still be potent. The heaviest mountain snow will be across
northern California and southwest Oregon during the day Friday.
With the influx of Pacific moisture, snow levels will rise to
between 3,000 and 4,000 ft in this region, which will still be
plenty low enough to impact the passes, especially when adding
dynamic cooling from any heavy snow on the windward side of the
mountains. 24 hour WPC probabilities for 6 inches or more through=20
Friday are above 50% from the southern Oregon Cascades through the=20
Sierras, with the Klamath Mountains of northern California over
80%.

The most potent upper level energy with this wave will track across
the Southwest Friday night, then rapidly translate eastward to
support the impressive cyclone across the northern Plains and upper
Midwest. This will result in a rapid collapse/weakening of any
organized precipitation across the Southwest during the day
Saturday. A smaller portion of the energy from the original second
wave will retrograde towards the Pacific Northwest and merge with a
third shortwave moving into the coast. This will keep valley rain
and mountain snow ongoing across much of Washington State, Oregon,
and Idaho Friday night into Saturday. The Cascades will be the
focus for the heaviest snow, with 24 hour WPC probabilities for 6
inches or more of snow above 50% for all of the Cascades, and up to
80% for much of the Oregon Cascades.

On Day 3/Saturday Night & Sunday, a fourth trough will approach the
Pacific Northwest in the form of a vertically stacked low. That low
will approach the coast of Washington and Oregon during the day
Sunday. Lingering lift from the previous wave will keep the=20
mountain snow continuing through Saturday night and intensify=20
during the day Sunday, especially across Oregon. It's here that=20
the low will eventually come ashore Sunday night. The greatest lift
and moisture flux will be during the day Sunday into Oregon ahead
of the low, so the heaviest precipitation associated with it will=20
be then.=20

Since the snow is unlikely to stop at all this weekend into the
Cascades, expect the highest elevations to pick up several feet of
snow through the period. The Sawtooths and Bitterroots of Idaho and
Montana as well as the Yellowstone N.P. area will also pick up=20
several feet of new snow through the weekend as the waves that
impact the coast earlier move inland across the Pacific Northwest
through the weekend.

Wegman


...Northern Plains...
Day 2...

...Rapidly deepening low and a transition from rain to a wintry mix
and eventually snow is expected to combine with very strong winds
to lead to possible blizzard conditions across parts of the=20
eastern Dakotas and western Minnesota. See Key Messages linked at=20
the bottom of the discussion for more information...

The southern stream closed low emerging from the Four Corners and
into the Southern Plains Friday morning will become a formidable
winter storm across the Plains Friday into Saturday. As this closed
low emerges into the Plains early Friday, it will continue to
deepen, featuring 500-700mb height anomalies by 00Z Saturday that
are below the minimum percentile within the CFSR climatology=20
between 850-500mb across a large portion of the Plains. This is an=20 exceptionally deep system, and the combination of the intense=20
height falls with the LFQ of a subtropical jet streak rotating=20
through the trough will result in rapid lee-cyclogenesis beginning=20
as early as Friday morning.=20

This surface low will deepen rapidly, approaching March record
pressure levels across the Plains as it tracks from eastern CO
Friday morning to eastern SD Friday evening, and then the U.P. of
MI Saturday aftn. While there is some uncertainty in the exact
placement and track of this low, especially with the potential for
numerous low-level centers to rotate around the broader area of=20
low pressure, the overall spread is relatively small. This leads=20
to high confidence in the storm's evolution and area most likely=20
to experience a brief period of heavy snow. With this low=20
deepening rapidly, significant moisture will be drawn northward=20
from the Gulf on impressive isentropic ascent, and the resultant=20
theta-e ridge is progged to lift into a robust TROWAL which will=20
pivot across WI and into MN/ND/SD Saturday morning. As this occurs,
the combination of increasing ascent, aided by a pivoting=20
deformation axis W/NW of the low center, and cooling of the column=20
through both dynamic affects and ageostrophic flow/cold air=20
drainage from the NNW, will result in a p-type transition from rain
to mixed to snow.

There remains uncertainty into how long this transition will take
to occur, but the intense omega into the column Saturday morning
suggests the guidance may be under-doing the speed at which this
occurs, indicating a faster transition from rain to snow, with less
freezing rain/sleet in between. This is more typical of the
conceptual model for this type of system as well, so while mixed
precip is likely at times, the more impactful wintry precipitation
type should be snow, which will likely come down heavy at times
(1-2"/hr rates). At the same time, very strong winds, which are=20
progged by model soundings to exceed 50 kts in the 800-900mb layer,
will help to fracture dendrites leading to low SLRs which will be=20
blow around considerably. Additionally, even with snow coming down=20
heavily it may struggle to accumulate for the first hour or so=20
given warm antecedent ground conditions and prior rainfall. So,=20
while total snowfall may be somewhat modest except beneath the=20
pivot point of this deformation axis, impacts will be substantial=20
with near blizzard conditions possible from far northeast Nebraska=20
through northern Minnesota. In this area, 24-hr WPC probabilities=20
from 00Z Sat to 00Z Sun reach as high as 50-70% for 4+ inches, and=20
isolated totals above 6 inches are possible (20-40%). Additionally,
some light freezing rain has a 10-30% chance of accumulating 0.1"=20
or more in a small portion of NW MN.

Snell/Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-C8iDBYFPoy5G9vFU9aA-6dFsvyULo9fMqdic9FGulkTk= 17C2BIIP0UDZ5srNUP5GTTtCZkqcftRY9HxSoF81s2y_vA$=20

$$

=3D =3D =3D
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FOUS11 KWBC 140655
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Fri Mar 14 2025

Valid 12Z Fri Mar 14 2025 - 12Z Mon Mar 17 2025

...The West...
Days 1-3...

The active pattern continues across the West with several days of
widespread wintry precipitation impacting much of the area through
the upcoming weekend.

The period begins with a potent closed mid-level low moving across
the Southern High Plains of CO/NM. This feature is quite intense,
reflected by NAEFS 850-500mb height percentiles that are below the
minimum in the CFSR climatology across a large, and expanding,
section of the country centered along the High Plains. As this
feature shifts E/NE this afternoon, it will continue to deepen and
produce near-blizzard conditions across the Northern Plains (more
on that in the section below). Behind this departing system, heavy
snow will continue across the Southern and Central Rockies through
D1 as a combination of mid-level deformation and a trailing cold=20
front overlap to enhance ascent in a region of still elevated 700mb
RH across the Four Corners and into Wyoming. While this snow=20
should wane quickly by 00Z Saturday, and snow levels will generally
be in the 5000-6000 ft range, snow is expected to accumulate=20
several additional inches D1 as reflected by WPC probabilities that
are high (>70%) for 4+ inches across the CO Rockies, the northern
Sangre de Cristos, and as far north as the Big Horn Mountains of
WY.

Any break in precipitation behind this significant, but departing,
system will be short lived as the active pattern sheds another
amplifying shortwave across the Pacific and into CA/OR by 00Z
Saturday /late D1/. This next impulse will be accompanied by an
impressive lobe of vorticity, with the resultant trough development
driving height falls once again from CA through the Four Corners
into D2. Available moisture with this next impulse is progged to=20
be much less than with the first shortwave, reflected by NAEFS PW=20
anomalies that are near normal east of AZ as the maximum IVT=20
downstream of this trough axis is modest (GEFS and ECENS=20
probabilities for 500 kg/m/s less than 10%) and focused generally=20
south into Mexico. Of course, this is pretty typical with ARs that=20
are oriented more W/NW than W/SW, but enough moisture and continued
lowered snow levels of generally 3000-5000 ft will allow for at=20
least modest snowfall accumulations. The heaviest snowfall=20
accumulations D1 into D2 are expected from the Sierra into the=20
Mogollon Rim and into the Four Corners, where WPC probabilities are
high once again for 8+ inches, and locally 1-2 feet is possible in
the Sierra and northern CA terrain near the Shasta/Trinity region.

Interestingly, as the second shortwave digs across the Four Corners
into D2, the upstream flow becomes more favorable for a surge of
moisture and heavy precipitation farther north into the Pacific and
Interior Northwest. A trough over British Columbia/Alberta
interacts with the trough moving across the Four Corners to squeeze
the flow over the Pacific, resulting in fast and zonal flow surging
into WA/OR. Impulses within this flow will help push two distinct
surface lows onshore, the first Saturday morning and the second
early Sunday morning, helping to enhance ascent. Regardless of
those surface lows, deep layer lift becomes impressive and moisture
increases as a strengthening Pacific jet streak pivots onshore and
begins to buckle, lifting meridionally on Sunday downstream of an
even more potent trough approaching the coast.=20

Both ECENS and GEFS probabilities exceed 70% for 500 kg/m/s IVT=20
reaching the coast D3, funneling moisture along a cold front which=20
will elongate into the region. Although the accompanying WAA with
this atmospheric river (AR) will drive snow levels to as high as
6000 ft D3 south of the cold front, considerable moisture and a
sharp gradient in snow levels will likely result in impactful
pass-level snow from the Cascades through the Northern Rockies,
with still impressive snow but generally above pass-levels farther
south from the Great Basin into the Central Rockies, as much of the
West is again covered in elevation-based snowfall. High WPC=20
probabilities (>70%) late D1 through D3 become widespread for 6+
inches each day from the OR Cascades northward into the Olympics
and WA Cascades, and as far east as the Salmon River/Sawtooth area,
north into the Northern Rockies, and even as far as the Tetons.
Event total snowfall is likely to be extreme in the higher terrain
of the OR Cascades where 4-6 feet of snow is possible, with
widespread 1-3 feet in the other higher elevations regions of the
Northwest.


...Northern Plains...
Days 1-2...

Rapidly strengthening low pressure in the lee of the Rockies this
morning will approach or exceed March sea-level pressure records
across the Northern Plains as it tracks northeast through Saturday
aftn. Not only will SLP records be approached, but 850-500mb height
anomalies are progged to fall below the all-time minimums within
the CFSR climatology according to NAEFS, further indicative of the
intensity of this system. The result of this evolution will be a=20
major winter storm impacting the Northern Plains late Friday=20
through Saturday.=20

As the surface low tracks northeast from the Central High Plains,
it will be driven by an overlap of impressive height falls
downstream of the primary closed low and at least modest upper
diffluence in the LFQ of a poleward arcing jet streak east of the
mid-level center. Together, these will drive intense deep layer
ascent aiding in the storm strengthening. At the same time,
confluent low-level flow east of the low will draw impressive=20
moisture northward on 300-305K isentropic ascent. This moisture
will surge am impressive theta-e ridge northward, which will then
rotate cyclonically and lift into a robust TROWAL, pivoting over
eastern NE, SD, ND, and western/central MN Saturday. At the same
time, an impressive deformation axis will overlap with this TROWAL,
supporting an intense axis of maximized ascent to drive heavy=20
precipitation rates.

Initially, the theta-e advection will surge warm air into the
region such that the column will support primarily rain. However,
as the low continues to deepen and move northeast, and mesoscale
ascent intensifies, the combination of dynamic cooling and
ageostrophic flow on NW winds into the low center will rapidly cool
the column. The guidance continues to suggest a period of mixed
precip, including sleet and freezing rain, will occur, but this
again appears to be a conceptual setup where the transition period
is quite rapid. This indicates that while some light icing is
possible, the predominant wintry p-type will be snow, which will
almost certainly become heavy at times (70% probabilities for 1"/hr
according to the HREF). This is supported as well by NAM cross-
sections indicating a region of theta-es lapse rates <0C/km in the
presence of symmetric instability, suggesting the potential for=20
CSI or even CI (thundersnow). Although antecedent conditions are=20
quite warm and some rain will begin this event, these rates should=20
quickly overwhelm this hostility leading to rapid snow=20
accumulation.=20

Finally, impacts during the period of heavy snow are likely to be
impressive due to strong winds that may gust above 50 mph during
the period of heavy snow. While the period of heavy snow rates is
likely to be somewhat temporally modest except beneath the pivot
point of the deformation axis, the overlap of extreme rates of
1-2"/hr and these strong winds will create near blizzard conditions
and extremely dangerous travel. Snowfall will begin late D1 but
accumulations are expected to be modest before 12Z Saturday as
reflected by WPC probabilities of 30-50% for just 2 inches across
far eastern SD. Early D2 snowfall coverage and intensity ramps up,
and WPC probabilities are high (>70%) for 4+ inches near the Coteau
des Prairies and as far north as International Falls, MN. Locally,
8 inches of snow is possible beneath the pivoting deformation,
especially should any thundersnow occur. Additionally, some light
icing across western MN has a 10-30% chance of reaching 0.1+" of
ice accretion.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5NiP0-ogg52fE6brKTWGycDa8ZLgcXm9WVPtJmLZMYtjB= Mz4CmSB-i13_PYTxzrwGiMEmxiTIy8klKrf4xHL-sy-xic$=20

$$

=3D =3D =3D
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FOUS11 KWBC 141851
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 PM EDT Fri Mar 14 2025

Valid 00Z Sat Mar 15 2025 - 00Z Tue Mar 18 2025


...Northern Plains...
Day 1...

Rapidly strengthening low pressure analyzed over the central Plains
this afternoon will approach or exceed March sea-level pressure=20
records across the Northern Plains as it tracks northeast through=20
Saturday aftn. Not only will SLP records be approached, but=20
850-500mb height anomalies are progged to fall below the all-time=20
minimums within the CFSR climatology according to NAEFS, further=20
indicative of the intensity of this system. The result of this=20
evolution will be a major winter storm impacting the Northern=20
Plains late Friday through Saturday with a combination of heavy=20
snow and gusty winds.

As the surface low tracks northeast from the Central High Plains,
it will be driven by an overlap of impressive height falls
downstream of the primary closed low and at least modest upper
diffluence in the LFQ of a poleward arcing jet streak east of the
mid-level center. Together, these will drive intense deep layer
ascent aiding in the storm strengthening. At the same time,
confluent low-level flow east of the low will draw impressive=20
moisture northward on 300-305K isentropic ascent. This moisture
will surge am impressive theta-e ridge northward, which will then
rotate cyclonically and lift into a robust TROWAL, pivoting over
eastern NE, SD, ND, and western/central MN Saturday. At the same
time, an impressive deformation axis will overlap with this TROWAL,
supporting an intense axis of maximized ascent to drive heavy=20
precipitation rates.

Initially, the theta-e advection will surge warm air into the
region such that the column will support primarily rain. However,
as the low continues to deepen and move northeast, and mesoscale
ascent intensifies, the combination of dynamic cooling and
ageostrophic flow on NW winds into the low center will rapidly cool
the column. The guidance continues to suggest a period of mixed
precip, including sleet and freezing rain, will occur, but this
again appears to be a conceptual setup where the transition period
is quite rapid. This indicates that while some light icing is
possible, the predominant wintry p-type will be snow, which will
almost certainly become heavy at times (70% probabilities for 1"/hr
according to the HREF). This is supported as well by NAM cross-
sections indicating a region of theta-es lapse rates <0C/km in the
presence of symmetric instability, suggesting the potential for=20
CSI or even CI (thundersnow). Although antecedent conditions are=20
quite warm and some rain will begin this event, these rates should=20
quickly overwhelm this hostility leading to rapid snow=20
accumulation.=20

Finally, impacts during the period of heavy snow are likely to be
impressive due to strong winds that may gust above 50 mph during
the period of heavy snow. While the period of heavy snow rates is
likely to be somewhat temporally modest except beneath the pivot
point of the deformation axis, the overlap of extreme rates of
1-2"/hr and these strong winds will create near blizzard conditions
and extremely dangerous travel. The changeover to snow will
commence across eastern SD after 06Z Saturday before expanding
north-northeast across western and north-central Minnesota between
12Z-18Z. Recent trends have shifted this band of heavy snowfall
amounts (>4") eastward by about 75 miles or so as guidance is=20
consolidating on a more compact area of low pressure across the=20
Upper Midwest. WPC probabilities for at least 4" are high (>70%)=20
across southwest to north-central Minnesota, with 40-70% chances=20
extending into far eastern South Dakota and far southeast North=20
Dakota. Locally, a narrow swath of at least 8" of snow is possible=20
(20-40%) beneath the pivoting deformation, especially should any=20
thundersnow occur. Additionally, some light icing across north-=20
central MN has a 10-30% chance of reaching 0.1+" of ice accretion.


...The West...
Days 1-3...

The active pattern continues across the West with two separate
systems producing widespread wintry precipitation across much of=20
the area through early next week.

After the significant winter storm departs into the central U.S.,=20
any break in precipitation across the West will be short lived as=20
the active pattern sheds another amplifying shortwave across CA/OR=20
tonight. This next impulse will be accompanied by an impressive=20
lobe of vorticity, with the resultant trough development driving=20
height falls once again from CA through the Four Corners on D1.=20
Available moisture with this next impulse is progged to be much=20
less than with the first shortwave, reflected by NAEFS PW anomalies
that are near normal east of AZ as the maximum IVT downstream of=20
this trough axis is modest (GEFS and ECENS probabilities for 500=20
kg/m/s less than 10%) and focused generally south into Mexico. Of=20
course, this is pretty typical with ARs that are oriented more W/NW
than W/SW, but enough moisture and continued lowered snow levels=20
of generally 3000-5000 ft will allow for at least modest snowfall=20 accumulations.

Interestingly, as this shortwave digs across the Four Corners, the
upstream flow becomes more favorable for a surge of moisture and=20
heavy precipitation farther north into the Pacific and Interior=20
Northwest. A trough over British Columbia/Alberta interacts with=20
the trough moving across the Four Corners to squeeze the flow over=20
the Pacific, resulting in fast and zonal flow surging into WA/OR.=20
Impulses within this flow will help push two distinct surface lows=20
onshore, the first Saturday morning and the second early Sunday=20
morning, helping to enhance ascent. Regardless of those surface=20
lows, deep layer lift becomes impressive and moisture increases as=20
a strengthening Pacific jet streak pivots onshore and begins to=20
buckle, lifting meridionally on Sunday downstream of an even more=20
potent trough approaching the coast.=20

Both 12Z ECMWF and GFS depict 500-700 kg/m/s IVT reaching the=20
coast D2, funneling moisture along a cold front which will=20
elongate into the region. Although the accompanying WAA with this=20 atmospheric river (AR) will drive snow levels to as high as 6000 ft south
of the cold front, considerable moisture and a sharp gradient in=20
snow levels will likely result in impactful pass- level snow from=20
the Cascades through the Northern Rockies and eventually Sierra
Nevada once again on D3, with still impressive snow but generally=20
above pass- levels farther south from the Great Basin into the=20
Central Rockies, as much of the West is again covered in elevation-
based snowfall. For the entire forecast period, high WPC=20
probabilities (>70%) for 8+ inches exist from the Sierra Nevada and OR
Cascades northward into the Olympics and WA Cascades, and as far=20
east as the Salmon River/Sawtooth area, north into the Northern=20
Rockies, and even as far as the Tetons. Event total snowfall is=20
likely to be extreme in the higher terrain of the OR Cascades where
4-6 feet of snow is possible, with widespread 1-3 feet in the=20
other higher elevations regions of the Northwest and Sierra Nevada.


Snell/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8IUy2IMH3gmbJPdc2_VgOZYyqx3DhlOaP9KWRE8dLibJp= kSro1W9Ydg1HuXjtsmvT9M_CoxSWv_e2bud9pzZyUug30I$=20

$$

=3D =3D =3D
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FOUS11 KWBC 150648
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 AM EDT Sat Mar 15 2025

Valid 12Z Sat Mar 15 2025 - 12Z Tue Mar 18 2025


...Northern Plains...
Day 1...

The rapidly strengthening low moving across the Northern Plains
which has been advertised the past few days will be well underway
at the start of the period. At 12Z Saturday, the surface low is
progged to be near the Twin Cities, MN, and will be lifting
northeast, reaching Ontario, Canada by 00Z Sunday. N and W of this
low center, a strong and pivoting deformation axis will be helping
to drive intense ascent, causing a changeover from rain to heavy
snow across western MN, resulting in blizzard, and near-blizzard,
conditions through the aftn.

Moisture advection downstream of this strengthening cyclone will
remain impressive through D1, with isentropic ascent surging the
accompanying theta-e ridge into a robust TROWAL which will pivot
cyclonically back into the Dakotas and Minnesota today. The overlap
of this enhanced moisture and the collocated deformation axis will
increase both moisture and ascent to cause a narrow stripe of heavy precipitation, changing rapidly from rain to snow. Dynamic cross-
sections across this region continue to suggest an axis of CSI/CI,
supported by the elevated instability within the TROWAL, to create
snowfall rates that are forecast both by HREF probabilities and the
WPC prototype snowband tool to reach 1-2"/hr. Despite hostile
antecedent conditions due to warm temperatures and rain, these
snowfall rates will rapidly accumulate, and when combined with wind
gusts of 50 mph, will likely result in blizzard and near-blizzard
conditions through the aftn. This is despite accumulations that
will in most areas be modest except within the stripe beneath the
pivoting deformation axis, where WPC probabilities are high (>70%)
for 4+ inches and locally as much as 8 inches is possible.


...The West...
Days 1-3...

The active pattern continues across the West with two separate
systems producing widespread wintry precipitation across much of=20
the area through early next week.

The next impulse within this active pattern will push an impressive
vorticity lobe eastward from OR through the Great Basin to start
Saturday morning, with the resultant trough development driving=20
height falls once again into the Four Corners on D1. PW anomalies=20
that are near normal east of this feature as the maximum IVT=20
downstream of this trough axis is modes and focused generally=20
south into Mexico, but available moisture is still sufficient for a
swath of moderate to heavy precipitation, with snow-levels
generally 3000-5000 ft allowing for moderate snowfall accumulations
above these levels. WPC probabilities D1 are moderate to high
(50-90%) for 4+ inches across the CO Rockies, Sangre de Cristos, White Mountains of AZ, and the Sacramentos.

As this lead shortwave digs across the Four Corners, the upstream=20
flow becomes more favorable for a surge of moisture and heavy=20
precipitation farther north into the Pacific and Interior=20
Northwest. A trough over British Columbia/Alberta interacts with=20
the trough moving across the Four Corners to squeeze the flow over=20
the Pacific, resulting in fast and zonal flow squeezing into=20
WA/OR. Impulses within this flow will help push two distinct=20
surface lows onshore, the first this morning and the second early=20
Sunday morning, helping to enhance ascent. Regardless of those=20
surface lows, deep layer lift becomes impressive and moisture=20
increases as a strengthening Pacific jet streak pivots onshore and=20
begins to buckle, lifting meridionally on Sunday downstream of an=20
even more potent trough approaching the coast.=20

Resultant IVT with this setup becomes moderate to strong once
again, potentially reaching 500-750 kg/m/s as moisture funnels
onshore along a cold front which will elongate into the region.=20
Although the accompanying WAA with this atmospheric river (AR) will
drive snow levels to as high as 6000 ft south of the cold front,=20 considerable moisture and a sharp gradient in snow levels will=20
likely result in impactful pass-level snow from the Cascades=20
through the Northern Rockies and eventually Sierra Nevada once=20
again later D2 into D3. Still impressive snow, but at generally=20
above pass-levels, is forecast farther south from the Great Basin=20
into the Central Rockies, as much of the West is again covered in=20 elevation-based snowfall. For the entire forecast period, high WPC=20 probabilities (>70%) for 8+ inches exist from the Sierra Nevada and
OR Cascades northward into the Olympics and WA Cascades, and as=20
far east as the Salmon River/Sawtooth area, north into the Northern
Rockies, and even as far as the Tetons. Event total snowfall is=20
likely to be extreme in the higher terrain of the OR Cascades where
4-6 feet of snow is possible, with widespread 1-3 feet in the=20
other higher elevations regions of the Northwest and Sierra Nevada.

During the latter half of D3 /Monday evening/ the parent trough
digging across CA and into the Great Basin responsible for the snow
axis shifting south into the Sierra late D2 will pivot eastward
towards the Four Corners/Central Rockies. This will bring a slow
end to precipitation across much of the West (at least briefly) but
may help to produce another significant central U.S. storm by the
middle of next week.


...Central Rockies and High Plains...
Day 3...

A shortwave emerging from the Pacific will amplify as it moves
across CA late Monday and then tracks progressively into the Great
Basin, reaching the Four Corners by the end of the forecast period.
This shortwave will be accompanied by an intensifying sub-tropical
jet streak which will begin to arc poleward downstream of this
amplifying trough. This will have the dual-pronged effect of
transporting moisture into the Central Rockies while also placing
favorable LFQ diffluence atop the region of greatest mid-
level height falls. The resultant deep layer ascent will likely
interact with a cold front dropping southeast into the area, and
the setup appears favorable for developing cyclogenesis in the
central High Plains by Tuesday morning. Where the strongest ascent
overlaps the greatest moisture, especially in areas of expanding
frontogenesis, a swath of heavy snow is likely. WPC probabilities
at this time are modest, just 30-50% for 2+ inches outside of
terrain features across WY, but are higher in the Big Horns and
Black Hills.=20

This system may become the next powerful cyclone across the Plains
through the middle of next week.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_G4_gqVRI09X9uf3k76Us6Lg-9FRQAPxhvOaXNqa_AGOO= LMDs44fpGtvqtamqFFLFc-ZlFsO6J7kRFr-2GBktzdIvSs$=20

$$

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FOUS11 KWBC 151842
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
242 PM EDT Sat Mar 15 2025

Valid 00Z Sun Mar 16 2025 - 00Z Wed Mar 19 2025


...Midwest to Great Lakes...
Day 1...

Recent trends have increased the potential for a swath of moderate
snowfall to occur on the backside of a developing secondary low
pressure system racing northward from the Mid- Mississippi Valley
this evening. The mechanism behind this trend is related to a
deepening shortwave crossing the southern Plains this afternoon and
becoming more separated from the exiting upper low over Minnesota.
This leads to increased ridging ahead of this secondary shortwave
(partly amplified by latent heat release from convection across
the South this afternoon) and a repositioning of the 250 mb jet
streak over the Upper Great Lakes to produce more favorable upper
divergence and a broader precipitation shield reaching westward
enough into the cold airmass settling in behind a potent cold front
crossing the region today. While this system will be very
progressive, there is potential for snowfall rates to approach
1"/hr from northern IL and eastern WI through the western L.P. and
eastern U.P. of MI between 06Z to 18Z Sunday. However, even though
this is a D1 forecast and snow begins to develop after 06z tonight
there remains more uncertainty than to be desired. Additionally,
most areas have surface temperatures well above freezing today and
will see precip type start out as rain, leading to possible heavy
snowfall rates driving where most accumulation occurs. WPC
probabilities for at least 4" have increased across the northern
L.P. of MI to around 30-50%, where the 12z HREF depicts the
greatest chances for 1"/hr snowfall rates. Lighter amounts under
3" are anticipated to stretch along a southwest- northeast corridor
from northern IL/southeast WI to the eastern MI U.P.


...The West...
Days 1-3...

The active pattern continues across the West with an atmospheric
river impacting the Oregon Cascades and California ranges through
D2 before the associated upper trough swings across the
Intermountain West and Rockies into D3.

As a shortwave impulse at the base of the upper trough approaches
the Northwest on Sunday the resultant IVT with this setup becomes
moderate to strong, potentially reaching 500-750 kg/m/s at the
start of D1 as moisture funnels onshore along a cold front which
will elongate into the region. Although the accompanying WAA with
this atmospheric river (AR) will drive snow levels to as high as
6000 ft south of the cold front, considerable moisture and a sharp
gradient in snow levels will likely result in impactful pass-level
snow from the Cascades through the Northern Rockies and eventually
Sierra Nevada once again on D2. In fact, NAEFS SAT depicts IVT
values above the 99th climatological percentile on Sunday extending
from the OR/CA coast through the northern Great Basin, further
highlighting the impressive moisture associated with this system.

For the entire forecast period (ending 00Z Weds), high WPC
probabilities (>70%) for 12+ inches exist across the Sierra Nevada
and northern CA ranges, OR Cascades, east to the Salmon
River/Sawtooth area and northern Rockies. Event total snowfall is
likely to be extreme in the higher terrain of the OR Cascades where
4-6 feet of snow is possible, with widespread 1-3 feet in the
other higher elevations regions of the Northwest, Sierra Nevada,
and northern Great Basin.


...Central Rockies and High Plains...
Day 3...

The system impacting the West through early D3 will begin to eject
into the central Plains by the end of the forecast period. This
shortwave will be accompanied by an intensifying sub- tropical jet
streak which will begin to arc poleward downstream of this
amplifying trough. This will have the dual-pronged effect of
transporting moisture into the Central Rockies while also placing
favorable LFQ diffluence atop the region of greatest mid- level
height falls. The resultant deep layer ascent will likely interact
with a cold front dropping southeast into the area, and the setup
appears favorable for developing cyclogenesis in the central High
Plains by Tuesday morning. Where the strongest ascent overlaps the
greatest moisture, especially in areas of expanding frontogenesis,
a swath of heavy snow is likely and at this time is centered over
central WY on Tuesday. WPC probabilities for at least 4" have
increased to 40-80% throughout much of central WY, but remain
higher for at least 6" (70%+) in the Big Horns, Black Hills,
central UT ranges and CO Rockies.


This winter storm may become the next powerful cyclone across the
Plains and Upper Midwest through the middle of next week. See WPC's
Extended Forecast Discussion for more information.


Snell






$$

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FOUS11 KWBC 160723
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EDT Sun Mar 16 2025

Valid 12Z Sun Mar 16 2025 - 12Z Wed Mar 19 2025


...Great Lakes...
Day 1...

Guidance continues to intensify secondary low pressure developing
across the Ohio Valley early this morning downstream of a potent
shortwave trough emerging from the MS VLY. The resulting
intensification of this surface low is partly due to more
impressive downstream ridging interacting with the shortwave as it
develops a negative tilt over MO/IL/IN. Height falls and the LFQ of
an almost due-north advecting jet streak will help lower surface
pressures, and the the surface low is progged to deepen rapidly as
it lifts across the L.P. of MI and into Ontario province.

Moisture downstream of this surface low will be impressive, with
isentropic ascent lifting north from the Gulf surging PWs to above
the 99th percentile across the Mid-Atlantic, with the increasing
cyclonic flow pushing the accompanying theta-e ridge westward into
Michigan as a modest TROWAL. The overlap of this TROWAL with an
intensifying deformation axis will result in impressive omega,
partially driven by an intersection of fgen into the DGZ, to cause
rapid cooling of the column and resultant heavy snowfall. The
system is progressive off to the northeast, so the duration of
heavy snow is likely to be limited, but both the HREF and WPC
prototype snowband tool indicate a corridor of 1+"/hr snowfall
rates across the western L.P. for the first 6-10 hours of the
forecast. While the intensity has gotten stronger with recent model
runs, the placement has been quite consistent, and despite
antecedent conditions that are not favorable for snow
accumulations, these intense rates should still result in several
inches of snowfall as reflected by WPC probabilities for 2+ inches
that range from 10-30% near Chicago, IL, to above 70% near Traverse
City, MI, with 4-6" possible in the vicinity of the latter.


...The West...
Days 1-3...

The period begins with the Pacific Coast sandwiched between an
anomalous ridge to the east across the Intermountain West, and an
amplifying trough well to the west over the Pacific Ocean. Between
these two features, pinched mid-level flow will surge moisture
eastward into the Pacific Northwest, with IVT progged to approach
750 kg/m/s, funneling along a cold front and focused into OR. As
the upstream trough over the Pacific deepens and pivots eastward,
it will shed periodic lobes of vorticity into the Northwest, with
an accompanying surface low likely moving towards the OR/CA
border at the start of D2 /12Z Monday/. This surface low will
briefly intensify ascent (which will already be impressive through
height falls, PVA, upslope flow, and LFQ jet-level diffluence),
while also pushing the strongest moisture channel southward into
CA. While this suggests the highest PW anomalies will pivot south
as well towards the Sierra, sufficient upper level flow will
maintain elevated moisture well inland through D2, providing the
impetus for continued moderate to heavy snowfall across the terrain as
far east as the NW WY ranges.

For D1, the heaviest snowfall is likely within the plume of highest
IVT along the cold front from the OR Cascades eastward into the
Salmon River/Sawtooth ranges, and south into northern CA and the
Sierra. Here, WPC probabilities are high (>70%) for more than 8
inches of snow, with locally 2-3 feet possible in the Cascades and
near the Shasta/Trinity region, although snow-levels indicate the
heaviest accumulations will remain above 5000 ft before falling in
tandem with weakening snow intensity. During D2, the heaviest snow
becomes primarily focused in the Sierra where a high risk (>70%)
is progged by WPC probabilities for more than 12 inches, leading to
2-day snowfall as much as 2-4 feet in the higher elevations above
4000 ft. This will still result in significantly impacted travel
across the Sierra passes Monday into Tuesday.

Most of the forcing and moisture advect east by D3, so heavy snow
should wane across much of the West as it focuses instead into the
Central Rockies, but additional snowfall of a few inches is
possible (10-30%) in the Wasatch and Northern Rockies.


...Central Rockies to the Central Plains...
Days 2-3...

The next in this impressive series of significant low pressure
systems to impact the Plains will develop late Monday in the
Central Rockies and then strengthen into the Central Plains
Tuesday.

This system will initially develop downstream of a large trough
which will cross out of CA and the Great Basin, reaching the Four
Corners states Tuesday morning. Downstream height falls and PVA
will help drive large scale ascent into the region, which will be
additionally enhanced by a subtropical jet streak strengthening
through the primary trough axis. As this jet streak pivots
poleward, the LFQ will overlap with the mid-level height falls to
help drive surface pressure falls, and lee cyclogenesis the latter
portion of D2 /after 00Z Tuesday/. However, this jet streak will
outrun the primary forcing in response to vorticity shedding
rapidly to the east, with secondary troughing and a more
pronounced, negatively tilted, trough developing over the Central
High Plains later Tuesday. This will result in secondary jet streak development, with even more impressive diffluence overlapping the
more structured height falls/mid-level divergence. It is this
secondary development around 00Z Wednesday that will potentially
become a powerful cyclone with heavy snow across the Central Plains
and into the Upper Midwest by the end of the forecast period.

Although the first low is weaker, it will interact with a cold
front dropping out of the interior Northwest, leading to some
enhanced ascent through fgen and upslope flow across Wyoming on D2.
Moisture streaming into the wave from the E/SE, as well as aloft
from the S/SW will manifest as precipitation across WY, but with
the heaviest snowfall likely occurring in the terrain of the Big
Horns, NW WY ranges, and along the axis of greatest fgen over
N-central WY D2. However, total snowfall is expected to be modest
this period except above 4000 ft in the NW WY ranges and Big Horns,
where WPC probabilities for 6+ inches are above 70%.

Then during D3, snowfall becomes much more expansive and heavy as
the secondary, stronger, low develops and spreads snow from the
Central Rockies into the Central Plains. There is still
considerable placement and intensity uncertainty as reflected by
broad spread in the D3-D4 clusters, but the GFS members appear to
be the deepest and fastest solutions, with the CMC/ECMWF ensembles
supporting slightly less spread and are favored at this time. With
significant spread still in place, WPC probabilities are somewhat
compromised, but still support a high risk (>70%) of 6+ inches from
the Wind Rivers through the Laramie Range and into much of the CO
Rockies where heavy snow rates are likely both through
fgen/upslope flow. Farther east, increasing deformation over the
Central Plains by the end of the period will result in increasing
coverage of heavy snowfall, and while current WPC probabilities for
4+ inches are only around 10% across NE/KS, these will likely
increase and spread northeast into D4.

Additionally, as this secondary low intensifies, the pressure
gradient is progged to become quite intense, regardless of the
model preference, and WSSI-P is already featuring a widespread
30-50% probability of moderate blowing snow impacts, suggesting
the potential for near-blizzard conditions in some areas, but those
details still need to be ironed out as the event approaches.


Weiss



$$

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FOUS11 KWBC 161948
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 PM EDT Sun Mar 16 2025

Valid 00Z Mon Mar 17 2025 - 00Z Thu Mar 20 2025


...The West...
Days 1-2...

The period begins with the Pacific Coast sandwiched between an
anomalous ridge to the east across the Intermountain West, and an
amplifying trough well to the west over the Pacific Ocean. Between
these two features, pinched mid-level flow will continue surge=20
moisture eastward into the Pacific Northwest during the early part
of D1, with IVT falling below 600 kg/m/s through this evening,=20
funneling along a cold front and focused into northern CA and the
northern Great Basin tonight. As the upstream trough over the=20
Pacific deepens and pivots eastward, it will shed periodic lobes of
vorticity into the Northwest, with an accompanying surface low=20
likely moving towards the OR/CA border Monday morning. This=20
surface low will briefly intensify ascent (which will already be=20
impressive through height falls, PVA, upslope flow, and LFQ jet-=20
level diffluence), while also pushing the strongest moisture=20
channel southward into the central Sierra Nevada. While this=20
suggests the highest PW anomalies will pivot south as well towards=20
the Sierra, sufficient upper level flow will maintain elevated=20
moisture well inland through the beginning of D2, providing the=20
impetus for continued moderate to heavy snowfall across the terrain
as far east as the NW WY ranges.

For D1, the heaviest snowfall is likely within the plume of highest
IVT along the cold front from the OR Cascades eastward into the
Salmon River/Sawtooth ranges, and south into central CA and the=20
Sierra. Here, WPC probabilities are high (>70%) for more than 8=20
inches of snow, with locally 1-2 additional feet possible in the=20
Cascades and near the Shasta/Trinity region, although snow-levels=20
indicate the heaviest accumulations will remain above 5000 ft=20
before falling in tandem with weakening snow intensity. During D2,=20
the heaviest snow becomes primarily focused in the Utah ranges and
western WY as the main axis of moisture slides inland with the
sharp upper trough, where probabilities for more than 8" of snow=20
are also high, mainly above 8000 ft.


...Central Rockies/Plains through the Upper Midwest...=20
Days 2-3...

Increasing potential for a strong winter storm to stretch from the
central High Plains to the Upper Midwest between Tuesday and
Wednesday, with blizzard conditions becoming increasingly likely.=20
See the latest Key Messages linked at the bottom of the discussion=20
for more information.

This system will initially develop downstream of a large trough
which will cross out of CA and the Great Basin, reaching the Four
Corners states Tuesday morning. Downstream height falls and PVA
will help drive large scale ascent into the region, which will be
additionally enhanced by a subtropical jet streak strengthening
through the primary trough axis. As this jet streak pivots
poleward, the LFQ will overlap with the mid-level height falls to
help drive surface pressure falls, and lee cyclogenesis on Tuesday.
However, this jet streak will outrun the primary forcing in=20
response to vorticity shedding rapidly to the east, with secondary=20
troughing and a more pronounced, negatively tilted, trough=20
developing over the Central High Plains later Tuesday. This will=20
result in secondary jet streak development, with even more=20
impressive diffluence overlapping the more structured height=20
falls/mid-level divergence. It is this secondary development around
00Z Wednesday that will potentially become a powerful cyclone with
heavy snow across the central Plains and into the Upper Midwest=20
through the end of the forecast period. 00Z NAEFS SAT depicts the=20
low pressure over Kansas Tuesday night below the 0.5th=20
climatological percentile and eventually PWs reaching above the=20
90th percentile across eastern Iowa and Wisconsin on Wednesday=20
where the stronger surge of southerly flow exists, further highlighting
the strength of this system for the time of year.

Although the first low is weaker, it will interact with a cold
front dropping out of the interior Northwest, leading to some
enhanced ascent through fgen and upslope flow across Wyoming on D2.
Moisture streaming into the wave from the E/SE, as well as aloft
from the S/SW will manifest as precipitation across WY, but with
the heaviest snowfall likely occurring in the terrain of the Big
Horns, NW WY ranges, and along the axis of greatest fgen over
N-central WY D2. However, total snowfall is expected to be modest
this period except above 4000 ft in the NW WY ranges and Big Horns,
where WPC probabilities for 6+ inches are above 70%.

Then during D3, snowfall becomes much more expansive and heavy as
the secondary, stronger, low develops and spreads snow from the
Central Rockies into the Central Plains and eventually the Upper
Midwest. There is still some placement and intensity uncertainty,=20
but it has gradually decreased today with subtle slowing of the=20
shortwave in the GFS/GEFS and faster ejection in the ECMWF. WPC=20 probabilities have increased somewhat and still support a high risk

70%) of 6+ inches from the Wind Rivers through the Laramie Range

and into much of the CO Rockies where heavy snow rates are likely=20
both through fgen/upslope flow. Farther east, increasing=20
deformation over the Central Plains and Upper Midwest by the end of
the period will result in increasing coverage of heavy snowfall=20
and rates of 1-2"/hr in the deformation axis northwest of the
strong surface low. Current WPC probabilities for at least 4" are=20
low (10-30%) from eastern Colorado through northern Kansas and=20
central Nebraska, before increasing to around 30-60% from eastern=20
Nebraska through north- central Iowa. Then, a more mature cyclone=20
and combination of WAA/deformation leads to higher probabilities=20
for 6"+ of snow from southeast Minnesota through central/northern=20
Wisconsin and the MI U.P., where the latest WPC chances are 40-60%.
One factor that may impede the higher end potential of snow with=20
this system is that temperatures will be very warm during the days=20
and even hours prior to snowfall development. Highs on Tuesday are=20
forecast to reach the 70s and 80s across the central Plains and=20
Midwest.

Additionally, as this secondary low intensifies, the pressure=20
gradient is progged to become quite intense, regardless of the=20
model preference, and WSSI-P is already featuring a widespread=20
40-70% probability of moderate blowing snow impacts, suggesting=20
the potential for blizzard conditions in some areas. Additionally,
decent overlap in ECMWF EFI snow and wind gust values in the
central Plains are usually a good indicator that impacts=20
associated with blowing snow are possible.


Snell/Weiss




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4G-JYdtnPmNaMvwNDamWE91hSM5-XSIp9aXWD1D2XznQT= v7iri2X1Cw8epp4MumpVVp8xxMW838T7jHXEEFvH6564_k$=20

$$

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FOUS11 KWBC 170755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Mon Mar 17 2025

Valid 12Z Mon Mar 17 2025 - 12Z Thu Mar 20 2025


...The West...
Days 1-3...

Shortwave trough positioned just west of northern CA at 12Z Monday
will deepen into a closed mid-level low as it advects onshore and
drops subtly southeast Monday morning. The core of this low is
progged to track across the northern Great Basin this evening, but
a strong lobe of vorticity immediately in its wake will dig farther
south, amplifying the trough axis into southern CA by the end of
D1. Downstream of this trough, squeezed mid-level flow will produce
moisture confluence, lying directly beneath a strengthening and
meridionally advancing subtropical jet streak. This setup will=20
support impressive moist advection, reflected by PWs surging to=20
above the 90th percentile across CA and the Great Basin according=20
to NAEFS ensemble tables.

Within this moistening column, and beneath the deep layer ascent, a
wave of low pressure will move southeast along a baroclinic=20
gradient/cold front that will be driven eastward by the parent=20
trough evolution. This will maintain the focus of greatest moisture
just south of the front, but will drive some enhanced mid-level=20
isentropic ascent above and behind the boundary. This additional=20
lift, combined with periods of upslope flow into terrain features,=20
will result in widespread precipitation D1 from the Cascades=20
southward through the northern CA terrain and into the Sierra, as=20
well as points well east across the Great Basin and into the=20 Wasatch/Tetons/Wind Rivers.=20

Snow levels will vary considerably across the West during this=20
period due to the passage of the cold front. However, within the
region of greatest moisture/ascent and heaviest resultant snowfall,
snow levels should be generally 4000-6000 ft from the Sierra=20
through the Great Basin and into the Central Rockies. Snow levels=20
crash behind the cold front, allowing for at least moderate=20
snowfall but with more substantial pass level impacts in its wake.=20
WPC probabilities for more than 6 inches of snow are moderate=20
(30-50%) D1 across the Sierra and WA Cascades, but high (>70%)=20
across the Wasatch and into portions of western WY.

Additionally, along this front, impressive 0-2km fgen and increased
low-level RH will move into a corridor of elevated instability (NAM
SBCAPE 100-400 J/kg). This will occur within a region of high SnSq
parameter above 2 from eastern NV Monday evening through UT, WY,
and CO by Tuesday evening. This setup could produce convective=20
snow showers or even snow squalls, which is additionally supported
by simulated reflectivity in the high-res guidance. While any snow
squalls won't produce tremendous snowfall amounts, dangerous travel
is likely through snow-covered roads and rapidly changing
visibility.

This first system moves into the Central Rockies during D2,
becoming a significant winter storm in the Plains, and leaving a
brief respite much of D2 across the West within this otherwise
continued active pattern. This break will be short lived, however,
as yet another strengthening mid-level trough moves across the
Pacific and approaches the Pacific Northwest D3, likely coming=20
onshore Wednesday evening. Although the guidance varies=20
considerably with timing of the associated mid-level waves within=20
this next trough, they all agree that it will be potent, and=20
potentially negatively tilted, as it moves onshore during D3. The=20
downstream affects of this will be increased synoptic lift through=20
mid-level divergence, height falls, and intensifying upper=20
diffluence, all to pivot renewed moisture and forcing back onshore.
The antecedent airmass is cool, so snow levels will are only=20
expected to rise to around 3500 ft within the core of the strongest
WAA, and otherwise be generally 2000-3000 ft, suggesting travel=20
across area passes will again become problematic. This feature will
likely be transient, but have sufficient moisture to produce heavy
snow once again from the Olympics and WA Cascades southward into=20
the Sierra, with some spill over occurring before the end of the=20
period as far east as the Salmon River/Sawtooth/Northern Rockies.

WPC probabilities for 6+ inches of snow on D3 feature a high risk=20

70%) across the Olympics, Cascades, and Shasta/Trinity region of=20

northern CA< with lower probabilities below 50% continuing into the
Sierra and east across parts of the higher elevations of Idaho.


...Central Rockies, Central Plains, Upper Midwest...=20
Days 1-3...

...Another significant winter system likely to bring blizzard=20
conditions to portions of the Plains and Upper Midwest...

This system manifests as two waves of low pressure, a modest lead
wave, followed immediately by the more impressive cyclone. These
will generate from an anomalous trough which will amplify across=20
the Four Corners Tuesday /D2/ leading to impressive height
anomalies that are progged to fall below the 1st climatological
percentile between 700-500mb across the Central Plains by
Wednesday. This deepening and intense amplitude will yield strong
downstream ascent through height falls and mid-level divergence,
and as the subtropical jet streak amplifies it will begin to shift
almost due poleward, placing intense LFQ diffluence atop the region
of greatest height falls.

Together this will produce an environment extremely favorable for a
rapidly deepening cyclone in the lee of the Rockies. However,
before this occurs, a weaker wave is progged to develop near SE WY
Tuesday morning in response to more modest height falls, but in the
presence of increased baroclinicity as a cold front drops southward
from the Northern Rockies/High Plains, aided by the ageostrophic
response (fgen) of the RRQ of a departing jet streak into the Great
Lakes. This first low will eject rapidly east and weaken, but the
strong ascent and plentiful moisture will create heavy snow across
the Central Rockies, especially in WY where low-level upslope
ascent into the best frontogenesis will produce heavy snow rates.
WPC probabilities for more than 4 inches of snow are high (>90%)
across much of NW WY and into the Big Horns, with some elevated
probabilities for 1-2" extending into the lower terrain of eastern
WY as well.

During D2, however, is when the significant low develops. As the
synoptic pattern evolves as described above, lee cyclogenesis will
occur, and this low will be located beneath extremely favorable
synoptic ascent for rapid surface height falls, and nearly all the
ensemble groupings suggest SLP falling to the 980s Wednesday
morning over IA. There is generally good clustering of the ensemble
member low-pressures, but D3 clusters still suggest that the GEFS
is a bit deeper and faster with the progression, although the
spread appears to have decreased in the past 24-hrs. This leads to
high confidence in a rapidly strengthening low pressure, with
moisture steadily increasing as 300K isentropic ascent surges=20
theta-e northward and into the system, eventually lifting into a=20
TROWAL to provide moisture and elevated instability.

As has been the case with the past few of these March systems, the
antecedent airmass is warm, and the moist/warm advection funneling
in the higher PW air will cause the precipitation to begin as rain=20
in many areas, especially outside of terrain and into the Plains.=20
However, this should have minimal affect on snowfall accumulations,
as extreme dynamic cooling combined with ageostrophic flow into=20
low and cold advection as the low moves east will cause a rapid=20
p-type transition from rain to snow, with snow likely becoming=20
quite heavy within the deformation axis NW of the low Wednesday.=20
Snowfall rates that may reach 1-2"/hr (or more? some signals for CI
in a deep and saturated DGZ over IA indicating possible thunder-
snow) will overcome the warm ground quickly. Thus, the limiting=20
factor to snowfall amounts appears to be more the speed of this=20
system as it remains progressive, and CIPS analogs indicate the=20
75th% is only generally 4-8", higher into WI/MI where leading jet-
streak snowfall may add on to amounts before the main system. This=20
is additionally reflected by WPC probabilities for 4+ inches that=20
are below 30% D2, but increase to greater than 70% from western IA=20
northeast into the U.P. of MI D3. These probabilities have trended=20
upward, and locally 6+ inches of snow is likely within this band.

Finally, despite snowfall that may be modest in many areas outside
of the Upper Midwest, the intense winds driven by 850mb northerly=20
flow of 60 kts will produce strong gusts for which DESI indicates=20
has a 90% chance of exceeding 35 mph, and even a 50% chance for 50=20
mph across the Plains. This has led to high (>70%) probabilities=20
for moderate blowing snow impacts from WSSI-P, and despite snow=20
that may start as the heavier/wet variety, will transition to=20
higher SLR and broken aggregates leading to likely blizzard=20
conditions in some areas, especially from central Kansas northeast=20
into southern Minnesota.

By the end of the forecast period, this low will be well into
Ontario, but lingering snow and gusty winds are expected to still
be ongoing across MI, with some lake-enhanced snow across the U.P.,
western L.P. and maybe even into northern Indiana into early D4.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-8C5lghvvNxUpy34AV8hH1D76lewHLCE8KC2CsIvSnZPq= vURcB7gVVxXBn4nsOvkj4FpvN_SWI3H4sRXWpOEAyZXSs4$=20

$$

=3D =3D =3D
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FOUS11 KWBC 172104
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
504 PM EDT Mon Mar 17 2025

Valid 00Z Tue Mar 18 2025 - 00Z Fri Mar 21 2025


...California, Great Basin, and Pacific Northwest...=20
Days 1 and 3...

Amplified trough along the northern CA coast this afternoon will
dig across the Desert Southwest through Tuesday before swinging
across the Great Plains. Moderate to heavy snow will shift down the
rest of the Sierra Nevada through this evening with probabilities=20
for an additional >6" after 00Z are 50-80% on the southern Sierra
with snow levels dropping from 6000ft to 3000ft. A reinforcing
shortwave shifts over the WA coast this evening providing lift and
enhancement to the onshore flow and moderate snow to the WA/OR
Cascades into Tuesday. Day 1 PWPF for >6" are 30-70% on the
central/southern WA and northern/central OR Cascades.

The cold front shifting inland ahead of this trough will cross from
eastern NV into UT this evening. Increasing frontal forcing, low=20
level moisture, and some instability (12Z HREF mean MUCAPE of 100-200
J/kg) will allow a snow squall potential along the frontal zone.
Expect brief bursts of accumulating snow and rapidly reduced
visibility, causing dangerous overland travel in snow squalls.
Otherwise, terrain enhancements to the flow from the large trough
will allow heavy snow to continue behind the front in eastern NV
and the ranges of UT where Day 1 PWPF for >8" are 40-80% above the
post-frontal snow levels of 3000-4000ft.

The next trough rotates around a Gulf of Alaska low, crossing the
PacNW coast late Wednesday which is then followed by prolonged
onshore flow/continual precip through this weekend. Snow levels
Wednesday night/Thursday fluctuate between 2500ft and 4000ft along
the length of the Cascades and the Klamath Mtns where Day 3 PWPF
for >8" is 40-80%.


...Central Rockies, HIgh Plains...=20
Days 1-2...

...Heavy snow tonight/Tuesday over the north-central High Plains
and WY/CO Rockies...

A wave ahead of the parent trough/low tracks over WY early Tuesday
with strong lee-side cyclogenesis on the south-central Plains (aka
KS) through Tuesday. 1025mb high pressure over the Canadian
Prairies allows a frontal focus for snow over the Bighorn Mtns east
to and north of the Black Hills late tonight, sagging south=20
through Tuesday. This leading swath of snow has increased in=20
intensity and coverage given strong dynamics to overcome marginal=20
thermal conditions (it is currently around 50F in the lower=20
elevations of this swath). Day 1 PWPF for >6" are 50-80% east of=20
the Bighorns into SD and 50-90% for >18" in the Bighorns themselves
with ideal backing flow from east to north encountering upslope on
the Bighorns with ample Pacific and Gulf moisture. The trough to=20
the south will allow heavy snow on the western slopes of the CO=20
Rockies Tuesday where Day 1.5 PWPF for >8" are 50-90%.


...Central Plains through Upper Midwest...
Days 2/3...

...Blizzard conditions for portions of the Central Plains into the
Upper Midwest Tuesday night into Wednesday night...

The trough takes on a negative tilt as it pushes over the south-
central Plains Tuesday night, closing into a mid-level low
Wednesday morning over Iowa before tracking northeast over MI
Wednesday night. Peak intensity of the surface low looks to be
around 985mb along the IA/MO border Wednesday morning which will
generate a powerful wind field.

As has been the case with the past few of these March systems, the
antecedent airmass is warm, and the moist/warm advection funneling
in the higher PW air will cause the precipitation to begin as rain=20
in many areas of the Plains. However, this should have minimal=20
affect on snowfall accumulations, as extreme dynamic cooling=20
combined with ageostrophic flow into low and cold advection as the=20
low moves east will cause a rapid p-type transition from rain to=20
snow, with snow likely becoming quite heavy within the deformation=20
axis NW of the low Wednesday. Snowfall rates of 1-2"/hr, possibly
higher in thundersnow, will overcome the warm ground/low level
thermals quickly. Thus, the limiting factor to snowfall amounts=20
appears to be more the speed of this system as it remains=20
progressive. Confidence continues to increase in a swath of >6"
snow from eastern Neb to Lake Superior with enhancements from the
lake on the Huron Mtns of U.P. where >12" is likely in Day 2, 2.5=20
PWPF.

More modest snow totals of 2-4" are likely from northern KS through
central Neb, though intense winds driven by 850mb northerly flow=20
of 60 kts will produce strong/damaging gusts and blizzard=20
conditions. Blizzard looks to be met well into the Upper Midwest
until the northern forests limit the blowing snow potential which
is highlighted well in the probabilistic WSSI.

Wrap around snow shifts over southern WI/northern IL/MI/IN
Wednesday night into Thursday, though the parent low shifting well
into Quebec by Thursday morning should limit snow potential.


Jackson



...Winter Storm Key Messages are in effect as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!76sopEbkEJd7dK1iYt_iVkTxW7d-9d5eQfjzBet-YWnbe= kADyvht8GHZALYuKoVdJS3K7qctsKY8604HWIv7ASbfgZw$=20

$$

=3D =3D =3D
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FOUS11 KWBC 180721
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Tue Mar 18 2025

Valid 12Z Tue Mar 18 2025 - 12Z Fri Mar 21 2025


...The West...=20
Days 1-3...

The period begins with an amplifying mid-level trough diving across
the eastern Great Basin and into the Four Corners, pushing a cold
front eastward into the Rockies. This front will have the=20
potential to produce scattered convective snow showers and snow=20
squalls this morning across UT/CO/WY as its forcing driven by 0-2km
fgen moves east into a region of at least modestly unstable air=20
(100-300 J/kg of SBCAPE) and increased low-level RH. While snow=20 accumulations from these squalls will be minimal, brief heavy snow=20
rates and gusty winds could produce dangerous travel through the=20
day.

Behind this front, remnant low to mid level fgen and increased
moisture will drive a swath of heavy snowfall across much of the CO
Rockies and northward into WY and the Black Hills of SD. Large
scale ascent through the height falls downstream of the parent
trough combined with this fgen will allow for some heavy snow
rates, especially into the terrain where upslope flow will
additionally produce lift. WPC probabilities D1 for more than 6
inches are high (>70%) across the Wasatch, CO Rockies, and much of
the terrain of WY where locally more than 12 inches is possible,
especially in the Big Horns. Where the most intense fgen is
progged, primarily along the MT/WY border (a bit north from
previous model cycles), some lower elevation snowfall is likely
which could accumulate 3-6" into the High Plains of southern MT.

As this trough moves into the Plains later D1, brief ridging
blossoms across much of the West bringing an end to precipitation.
However, this respite will be relatively short lived as yet another
deepening trough approaches from the Pacific and moves onshore
Wednesday night. Height falls, PVA, and LFQ diffluence ahead of an
accompanying jet streak will all provide deep layer lift, aided by
upslope ascent as the low-to-mid level flow south of the trough
becomes more zonally oriented. This overlap of zonal/broadly
confluent mid-level flow beneath the upper jet streak will pivot
IVT exceeding 250 kg/m/s onshore, leading to an expanding plume of precipitation beginning Wednesday night /late D2/, and continuing
into D3. Snow levels during this period will be rather low,
starting around 2000-2500 ft, and warm only slowly, reaching
3500-4000 ft by the end of the forecast period. This suggests that
pass-level impacts are likely, and where the most intense ascent
occurs, even the lower valleys could receive some light snow
accumulations.=20

WPC probabilities for heavy snow exceeding 4 inches on D2 reach
above 70% from the northern CA terrain northward through the
Cascades and into the Olympics. On D3, moisture shunts north and
east just a bit, causing a wane in precip over the Sierra, but
expanding WPC probabilities for more than 4 inches from the
Olympics and Cascades east as far as the NW WY ranges and CO
Rockies where they exceed 70% in the higher terrain (especially in
the Cascades, Tetons, and Park Range of CO).


...Central High Plains through the Great Lakes...=20
Days 1-2...

...Significant storm system to bring blizzard conditions to
portions of the Central Plains and Upper Midwest. Key Messages are
in effect for this event...

This system will emerge in response to an amplifying mid-level
trough which will be crossing the Great Basin and approaching the
Four Corners starts to start the period /12Z Tuesday/. This trough
will continue to deepen in response to a sharp shortwave trough and accompanying vorticity lobe swinging through its base, such that=20
by the time it tracks into the Plains Wednesday, 850-700mb heights=20
fall below the minimum within the CFSR climatology according to=20
NAEFS, with 500mb heights dropping below the 2.5 percentile. This=20
is indicative of an exceptionally strong system producing intense=20
synoptic ascent. While height falls and PVA will drive a=20
considerable portion of the deep layer lift, a collocated=20
subtropical jet streak intensifying downstream and gaining rapid=20
latitude (arcing poleward) will place impressive LFQ diffluence=20
atop the region of greatest height falls. This setup will support=20
lee cyclogenesis with rapid intensification, and NAEFS mean MSLP=20
progs suggest that by 12Z Wednesday, this event has a 75-90% chance
of reaching an extreme minimum pressure.

Intense low pressures in March are not exceedingly rare, but this
one will likely result in a wide swath of heavy snow and strong
winds, producing blizzard conditions across the Plains and Upper
Midwest. While there is some uncertainty still among the various
model clusters as to the exact temporal and spatial evolution,
confidence is high that after some heavy snow in the Rockies D1, a
swath of blizzard conditions will develop farther east.=20

This will result in heavy snow developing first across KS/NE late=20
Tuesday night/early Wednesday morning, and then shifting northeast=20
through Wednesday across IA, SD, MN, WI, and finally the U.P. of=20
MI. During this time, the robust moisture funneling northward on=20
300K isentropic ascent will rotate into a strong TROWAL, helping to
support elevated instability and increased moisture. Where the=20
TROWAL is most impressive and lies atop the strongest deformation=20
from eastern NE through northern WI, cross-sections continue to=20
indicate a risk for CI and thundersnow. This will support snowfall=20
rates that have high chance for exceeding 1"/hr and 2"/hr (90% and=20
60% chance, respectively, from the HREF), which is supported as=20
well by the WPC prototype snowband tool. Where CI occurs, rates=20
could reach 3"/hr, and this will be more than sufficient to=20
overcome hostile antecedent conditions.

While some snow may initially melt, snow accumulation will likely
become rapid as SLRs rise due to cooling despite dendritic
fracturing on winds as high as 60 kts below the DGZ. This will
produce blizzard conditions, and the WSSI-P is forecasting a 90%
chance of moderate impacts, and 20% chance of major impacts, even=20
where snow amounts are more modest due to the speed of this system.
As far as snowfall amounts, WPC probabilities have increased, and
while are modest D1, are high (>70%) D2 for more than 6 inches from
far eastern NE through a continuous, but narrow, corridor as far
north as the central U.P. of MI. In this corridor, WPC
probabilities for 12+ inches have increased to as high as 30-50%,
highest from NW IA through the U.P., and WSE plumes indicate a
potential for up to 15" in some areas should this band translate
temporally over some areas a bit longer. Some higher snow totals
are also possible in the Huron Mountains of the U.P. where the
deformation axis and some lake enhanced snowfall combine.

By D3 this entire system shifts well east as the primary low moves
into Ontario and the accompanying cold front surges into the Mid-
Atlantic states. While some wrap-around snowfall will likely
continue through early Thursday, especially where lake enhancement
can occur across the U.P. and northwest L.P. of MI, as well as S/E
of Lake Michigan, additional accumulations are expected to be=20
modest, but have a low chance (10-30%) of exceeding 4 additional
inches in the U.P. and far NW lower Michigan near Traverse City.


...Interior Northeast...
Day 3...

Guidance has trended stronger with a developing low pressure
Thursday evening across the northern Mid-Atlantic states. While
there is still considerable uncertainty at this time range in the
strength of this system, most ensemble systems indicate a rapidly
developing low pressure between 00Z Friday and 12Z Friday lifting
across southern New England.=20

The synoptic setup is favorable for this development. The same
trough responsible for the Plains/Midwest blizzard will continue to
shift east, and while the primary shortwave will lift into Canada,
a secondary southern impulse is progged to deepen over the Central Appalachians. This vorticity lobe will help split the jet stream,
leading to an increasingly coupled pattern as the subtropical jet
streak pivots over the Carolinas and the polar jet stream lifts
towards Greenland. The LFQ of the former and the RRQ of the latter
will overlap the greatest height falls, indicating a strong
likelihood of low development along a surface cold front/baroclinic
gradient. By 12Z Friday, the deterministic global models prog SLP
to be sub 990mb, and this rapid intensification within the synoptic
setup will likely cause a strong deformation axis to develop NW of
the surface low. While the antecedent column is marginal for wintry precipitation, strong ascent in the vicinity of this deformation
will result in rapid dynamic cooling, and rain changing to snow,
possibly heavy, across Upstate NY and interior New England.

Being 6th period, confidence in amounts and placement is still
modest, but a band of heavy snow is becoming more likely, with
significant accumulations possible, especially in higher terrain.
This is reflected by current WPC probabilities that are above 50%
for 2 inches and 10-30% for 4 inches, highest in the Adirondacks
and Catskills.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8Yoi7m5O-gBf-TFjhMIUArgMGax2p9dPV5GajNsxk5OeN= fbTd57BRyE5cSgTpi5k87CL0aGohydHKsBTnDFTJSDCsOw$=20

$$

=3D =3D =3D
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FOUS11 KWBC 181921
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EDT Tue Mar 18 2025

Valid 00Z Wed Mar 19 2025 - 00Z Sat Mar 22 2025


...The West...=20
Days 1-3...

Assessment of the latest WV satellite indicates our deep upper
trough located just north of the Four Corners with primary ascent
pattern located in-of far eastern UT, southern WY, and the western
half of CO. Radar trends have materialized as previously forecasted
with scattered bouts of snow showers/squalls located within the
above areas due to the combination of robust mid-level ascent and
the progression of a surface cold front propagating eastward out of
the Great Basin through the Inter-Mountain West with the current
surface analysis indicating the position over western CO and NM.
Elevations above 5500' MSL will be the greatest beneficiaries of
heavier snowfall totals with the latest WPC probabilities for at
least 6 inches located over the interior of CO with >50% probs
located in those higher terrain locales along and west of the
Central Rockies. When coupled with the snow that has already
fallen, totals exceeding 12 inches will be plausible, especially
above 9500' MSL.

As this trough moves into the Plains later D1, brief ridging
blossoms across much of the West bringing an end to precipitation.
However, this respite will be relatively short lived as yet another
deepening trough approaches from the Pacific and moves onshore
Wednesday night. Height falls, PVA, and LFQ diffluence ahead of an
accompanying jet streak will all provide deep layer lift, aided by
upslope ascent as the low-to-mid level flow south of the trough
becomes more zonally oriented. This overlap of zonal/broadly
confluent mid-level flow beneath the upper jet streak will pivot
IVT exceeding 250 kg/m/s onshore, leading to an expanding plume of precipitation beginning Wednesday night /late D2, and continuing=20
into D3. Snow levels during this period will be rather low,=20
starting around 2000-2500 ft, and warm only slowly, reaching=20
3500-4000 ft by the end of the forecast period. This suggests that=20 pass-level impacts are likely, and where the most intense ascent=20
occurs, even the lower valleys could receive some light snow=20 accumulations.=20

WPC probabilities for heavy snow exceeding 4 inches on D2 reach
above 70% from the northern CA terrain northward through the
Cascades and into the Olympics. On D3, moisture shunts north and
east just a bit, causing a wane in precip over the Sierra, but
expanding WPC probabilities for more than 4 inches from the
Olympics and Cascades east as far as the NW WY ranges and CO
Rockies where they exceed 70% in the higher terrain (especially in
the Cascades, Tetons, and Park Range of CO).

Weiss/Kleebauer

...Central High Plains through the Great Lakes...=20
Days 1-2...

...Significant storm system to bring blizzard conditions to
portions of the Central Plains and Upper Midwest. Key Messages are
in effect for this event...

This system will emerge in response to an amplifying mid-level
trough which will be crossing the Great Basin and approaching the
Four Corners starts to start the period /12Z Tuesday/. This trough
will continue to deepen in response to a sharp shortwave trough and accompanying vorticity lobe swinging through its base, such that=20
by the time it tracks into the Plains Wednesday, 850-700mb heights=20
fall below the minimum within the CFSR climatology according to=20
NAEFS, with 500mb heights dropping below the 2.5 percentile. This=20
is indicative of an exceptionally strong system producing intense=20
synoptic ascent. While height falls and PVA will drive a=20
considerable portion of the deep layer lift, a collocated=20
subtropical jet streak intensifying downstream and gaining rapid=20
latitude (arcing poleward) will place impressive LFQ diffluence=20
atop the region of greatest height falls. This setup will support=20
lee cyclogenesis with rapid intensification, and NAEFS mean MSLP=20
progs suggest that by 12Z Wednesday, this event has a 75-90% chance
of reaching an extreme minimum pressure.

Intense low pressures in March are not exceedingly rare, but this
one will likely result in a wide swath of heavy snow and strong
winds, producing blizzard conditions across the Plains and Upper
Midwest. While there is some uncertainty still among the various
model clusters as to the exact temporal and spatial evolution,
confidence is high that after some heavy snow in the Rockies D1, a
swath of blizzard conditions will develop farther east.=20

This will result in heavy snow developing first across KS/NE late=20
Tuesday night/early Wednesday morning, and then shifting northeast=20
through Wednesday across IA, SD, MN, WI, and finally the U.P. of=20
MI. During this time, the robust moisture funneling northward on=20
300K isentropic ascent will rotate into a strong TROWAL, helping to
support elevated instability and increased moisture. Where the=20
TROWAL is most impressive and lies atop the strongest deformation=20
from eastern NE through northern WI, cross-sections continue to=20
indicate a risk for CI and thundersnow. This will support snowfall=20
rates that have high chance for exceeding 1"/hr and 2"/hr (90% and=20
60% chance, respectively, from the HREF), which is supported as=20
well by the WPC prototype snowband tool. Where CI occurs, rates=20
could reach 3"/hr, and this will be more than sufficient to=20
overcome hostile antecedent conditions.

While some snow may initially melt, snow accumulation will likely
become rapid as SLRs rise due to cooling despite dendritic
fracturing on winds as high as 60 kts below the DGZ. This will
produce blizzard conditions, and the WSSI-P is forecasting a 90%
chance of moderate impacts, and 20% chance of major impacts, even=20
where snow amounts are more modest due to the speed of this system.
As far as snowfall amounts, WPC probabilities have increased, and
while are modest D1, are high (>70%) D2 for more than 6 inches from
far eastern NE through a continuous, but narrow, corridor as far
north as the central U.P. of MI. In this corridor, WPC
probabilities for 12+ inches have increased to as high as 30-50%,
highest from NW IA through the U.P., and WSE plumes indicate a
potential for up to 15" in some areas should this band translate
temporally over some areas a bit longer. Some higher snow totals
are also possible in the Huron Mountains of the U.P. where the
deformation axis and some lake enhanced snowfall combine.

By D3 this entire system shifts well east as the primary low moves
into Ontario and the accompanying cold front surges into the Mid-
Atlantic states. While some wrap-around snowfall will likely
continue through early Thursday, especially where lake enhancement
can occur across the U.P. and northwest L.P. of MI, as well as S/E
of Lake Michigan, additional accumulations are expected to be=20
modest, but have a low chance (10-30%) of exceeding 4 additional
inches in the U.P. and far NW lower Michigan near Traverse City.

Mullinax

...Interior Northeast...
Day 3...

Guidance has backed off on the potential across the Interior
Northeast, in-line with the current ML output with subsequent prob
fields degraded compared to previous forecast. The threat for
surface cyclogenesis is still prevelant off the coast of Southern
New England with most of the deterministic running between
990-994mb as of 12z Friday. Despite deepening within the remainder
of the Friday window, the progressive nature of the precip and
marginal thermals currently depicted may limit the greatest threat
for at least 4" to the highest elevations in Northern New England
(Green and White Mountains) with very little chances in the
valleys. Threat for at least 2" is still running between 30-50% for
the Adirondacks and 50-70% for the Green/White Mountains, so the
threat is not muted by any stretch. Considering the potential
hovering near the threshold for impactful snowfall across the
Interior Northeast, will maintain close assessment of any trends as
we move through mid-week.=20

Kleebauer


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5eSpw51GHOXLBKXtAvn3NXL3mW0EEC916Q6UYG90Y9-5V= jumPAxuBz2YnIZZgM8LZg9il9J-lnBSHg6svoMn7FlEv5M$=20

$$

=3D =3D =3D
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FOUS11 KWBC 190719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Wed Mar 19 2025

Valid 00Z Wed Mar 19 2025 - 00Z Sat Mar 22 2025


...Pacific and Interior Northwest...
Days 1-3...

The seemingly never-ending training of shortwaves and moisture
continues this week across the Northwest CONUS.

The first of these will be the most potent, as a strong shortwave
trough pushes onshore this evening with a subtle negative tilt.
Impressive height falls ahead of this trough will drive ascent,
aided by at least weak LFQ diffluence as a streak pivots through
the base of this trough. Together, this will produce deep layer
lift from the northern Sierra through the Cascades and into the
Interior Northwest, supporting heavy precipitation as IVT surges
northeast on downstream S/SW flow. Snow levels will gradually rise
within the IVT core due to accompanying WAA, before falling again
with the passage of a cold front later D1. Despite this, snow
levels will generally be quite low through the period as the region
remains cold, rising from around 2500 ft to 3500 ft, before
crashing again to 2000-2500 ft behind the cold front. This suggests
that snow will impact many of the Cascades and northern CA Passes,
as well as into the interior NW causing hazardous travel. This
first system is progressive, however, and WPC probabilities peak
around 70% for 6+ inches in the highest peaks of the WA Cascades
and Olympics, with generally 4 inches or less forecast elsewhere.

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will
maintain onshore moisture advection to support rounds of
precipitation into the Northwest, with periodic vorticity lobes
swinging eastward (although maintaining latitude generally north of
OR) to enhance ascent. Snow levels D2-3 will fluctuate generally
between 2500ft and 4500ft, with rounds of precipitation leading to
periods of heavy snowfall. WPC probabilities both D2 and D3 are
similar in magnitude and areal extent, reaching 70% or more for 4+
inches from the Olympics, to the WA/OR Cascades, eastward through
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.
2-day snowfall in some of the higher elevations could reach 2-4
feet, with up to 1 foot at the higher passes of the Cascades.


...Central High Plains through the Great Lakes...=20
Days 1-2...

...Significant storm system to bring blizzard conditions to
portions of the Central Plains and Upper Midwest. Key Messages are
being issued for this system...

The low-pressure which has been progged for several days now to
deepen in the Central High Plains is taking shape this morning
noted by pressure falls and increasing convective elements across
CO/KS/NE. The parent PV anomaly is clearly noted in satellite
imagery across far SE CO and into the OK Panhandle, which is
generally S/SW of all available guidance. This suggests that the
E/SE trend that began 24 hours ago is valid, and the event may end
up even farther SE than the 00z suite of models. While the exact
track will be critical to the placement of the most significant
impacts related to this blizzard, a large scale significant event
is still likely from the Central High Plains northeast into the
Great Lakes.

As this low deepens today in response to favorable synoptic and
mesoscale ascent, precipitation will expand downstream. Current WV
imagery shows both the low and mid level moisture streaming into
the developing cyclone, and where isentropic ascent lifts into the
intensifying deformation axis, impressive omega will squeeze out
all available moisture in the form of heavy rain and snow. The
deformation axis on the NW side of this system will likely be quite
intense, and will be overlapped by a cyclonically surging TROWAL to
enhance both ascent and instability. Where this occurs, any rain
will quickly change to snow through dynamic cooling, and then come
down extremely heavily, reaching 2-3"/hr at times where CI
(thundersnow) can occur. This is supported by HREF 1"/hr and 2"/hr probabilities that reach 90% and 70%, respectively, and by the WPC
prototype snowband tool that suggests locally 3"/hr is possible
(20%).=20

These snowfall rates will quickly overwhelm hostile antecedent=20
conditions (some places were near 80 degrees Tuesday and will get=20
heavy snow today!), and WPC probabilities have increased for=20
significant snowfall despite the SE shift. The heaviest=20
accumulations are likely from central NE through NW IA where the=20
environment supports a pivoting deformation band, and WPC
probabilities are high (>70%) for at least 8 inches. Here, locally
12-15 inches is possible (30%) in some locations. Farther=20
downstream, the band will begin to translate more quickly, limiting
the duration of these intense rates, but still heavy snowfall is=20
likely as reflected by WPC probabilities that are high (>70%) for=20
6+ inches from SE Minnesota through the central U.P. of Michigan.=20 Additionally, strong winds of 50 mph or more will accompany this=20
snowfall, so despite SLRs that will generally be below climo, and=20
will start as a heavy/wet snow, as SLRs climb and aggregates=20
fracture, blizzard conditions are expected which will make travel=20
almost impossible in some areas.

Another interesting development that has shown up tonight is for a
secondary deformation axis to potentially develop in the vicinity=20
of the primary PV anomaly behind the surface low, bringing some=20
heavy snow rates of around 1"/hr from SE Iowa to the Chicago metro=20
area. While this is not expected to be as impressive as the axis to
the NW, moderate snowfall accumulations for which WPC=20
probabilities indicate have low chance (10-30%) of exceeding 4=20
inches, which when combined with gusty winds could still produce=20
moderate travel impacts.

This entire system exits quickly on Thursday, with some residual
deformation snow pivoting across lower Michigan, and some northern
flow in its wake leading to lake enhanced snowfall across the U.P.
and southeast of Lake Michigan. Still, additional snowfall should=20
be modest as reflected by WPC probabilities that are just around=20
10% for an additional 2 inches of snow in these areas.



...Interior Northeast...
Days 2-3...

Shortwave energy moving into the Mid-Atlantic will cause a split
jet stream (one rotating across the Carolinas while another pivots
towards Greenland) resulting in a modestly coupled structure to=20
help deepen a surface low south of New England beginning Thursday=20
night. The guidance has trended maybe just a bit weaker with this=20
low the past 24-hrs, but ensemble low points still agree in a=20
deepening system to around 990mb tracking from norther NJ to Cape=20
Cod and then into the Gulf of Maine by Saturday morning.=20
Uncertainty in the intensity and track remains, but spread is=20
relatively minimal for this time range, and deformation developing=20
on the NW side of this low is still likely to result in an axis of=20
rain changing to heavy snow. The GFS remains the deepest solution=20
and is somewhat discounted based on recent upstream performance,=20
but all the guidance indicates that an axis of sloped 850-700mb=20
fgen will drive omega into the deepening DGZ early Friday through=20
Friday night, which will dynamically cool the column to produce an=20
axis of heavy snowfall rates. The antecedent conditions are not=20
ideal for snow accumulations due to warm temperatures and rain, but
higher elevations of the interior Northeast from Upstate NY=20
through Maine could still see impactful accumulating snow.=20
Confidence is low, and trends for this event need to be monitored=20
over the next few model cycles, but WPC probabilities are modest at
just 10-30% for 4+ inches of snow in the higher elevations.


Weiss



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-KLFzRwvwe_9O_S-S3pOcQrHTcoe2AninTVhdXTk6G8_-= t5JWsp9HrgzSQesCEDSrA4t-02j4-CJfJuCIcAj1l-C19A$=20

$$

=3D =3D =3D
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FOUS11 KWBC 191857
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 PM EDT Wed Mar 19 2025

Valid 12Z Wed Mar 19 2025 - 12Z Sat Mar 22 2025


...Pacific and Interior Northwest...=20
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific=20
Northwest and Interior mountains in-of ID/MT/WY over the next 72=20
hrs. Current WV satellite imagery shows a fairly robust upper trough=20
located off the Pacific Northwest coast with a well-defined=20
diffluent structure on the eastern flank of the trough axis. The=20
ridge that has been present downstream is beginning to feel the=20
affects of the upstream disturbance leading to some flattening of=20
the northern ridge extension and a realignment of the ridge further=20
east. This general synoptic progression will lead to increasing mid=20
and upper ascent focused over a large portion of the west coast with=20
the primary impacts focused over Northern CA up through much of=20
OR/WA state. The beneficiary of the heaviest precip core over the=20
course of D1-2 will be situated within the Cascades with snow levels=20 hovering between 3000-4000' MSL prior to the stronger height falls=20
that will occur as the shortwave progresses towards the coast with=20
the mean trough taking on a more negative tilt as it eventually=20
ejects inland later this evening. The cold frontal progression=20
associated with the disturbance will move ashore around the time of=20
the mean trough swinging inland generating a period of falling=20
heights with snow levels dropping closer to 2000-3000' MSL leading=20
to snow accumulations becoming more prevalent in the higher valleys=20
around the Olympic Peninsula and Cascades. Snowfall accumulations of=20
at least 4" remain very high probabilistically (>70%) across the=20
higher elevations of the Cascades and Olympics in WA/OR, as well as=20
the Salmon, Siskiyou and Mount Shasta regions of CA. Mid-level probs=20
between 40-60% for at least 4" are located over the Northern=20
Sierra's with the highest chance in elevations above 7500' MSL.=20

Further inland, the prospects for heavy snow continue later this=20
evening as the shortwave propagates through WA/ID with the greatest=20
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the=20
Interior Northwest with the southern extent benefiting the Absaroka=20
Range of northwest WY. Similar probs of >70% for at least 4" of=20
snowfall exist in those terrain focused regions with the impacts=20
falling within the back-half of D1 into much of D2.=20=20


As this first trough shifts eastward, forcing will weaken across the=20 Northwest, but flow across the Pacific becomes increasingly zonal=20
due to squeezing between broad ridging well west off Baja and a=20
modest trough across the Gulf of Alaska. This zonal flow will=20
maintain onshore moisture advection to support rounds of=20
precipitation into the Northwest, with periodic vorticity lobes=20
swinging eastward (although maintaining latitude generally north of=20
OR) to enhance ascent. Snow levels D2-3 will fluctuate generally=20
between 2500ft and 4500ft, with rounds of precipitation leading to=20
periods of heavy snowfall. WPC probabilities both D2 and D3 are=20
similar in magnitude and areal extent, reaching 70% or more for 4+=20
inches from the Olympics, to the WA/OR Cascades, eastward through=20
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.
2-day snowfall in some of the higher elevations could reach 2-4=20
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...=20
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this=20
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous=20
cases of thundersnow, and prolific snowfall rates of 1-2"/hr=20
beneath the TROWAL over northern Kansas and eastern Nebraska. As=20
the 700mb low traverses northern Missouri this afternoon, a ribbon=20
of 700mb FGEN will pivot and extend over northwest Iowa, southeast=20 Minnesota, and as far north and east as northern Wisconsin.=20
Blizzard conditions will be most common from eastern Nebraska to=20
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"=20
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph=20
are likely in southeast Nebraska and into east-central Kansas. WPC=20
continues to issue Key Messages for the ongoing winter storm and=20
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region=20
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could=20
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine=20
should come to an end Friday night. WPC probabilities shows=20
moderate-to- high chances (40-70%) for snowfall totals >2" in the=20
peaks of the Catskills, Adirondacks, Berkshires, Green, and White=20
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday afternoon.=20

Mullinax



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_tUeCUIUvOwvMaOg6Kt0mVtMIBlbrkQsWTX7P7xqxAUWE= Dw9o0YHoj3fUUfj2w62dI5tqhx1cW-rM0aAkACbdxMyXnU$=20

$$

=3D =3D =3D
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FOUS11 KWBC 191913
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Wed Mar 19 2025

Valid 00Z Thu Mar 20 2025 - 00Z Sun Mar 23 2025


...Pacific and Interior Northwest...=20
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific=20
Northwest and Interior mountains in-of ID/MT/WY over the next 72=20
hrs. Current WV satellite imagery shows a fairly robust upper
trough located off the Pacific Northwest coast with a well-defined
diffluent structure on the eastern flank of the trough axis. The=20
ridge that has been present downstream is beginning to feel the=20
affects of the upstream disturbance leading to some flattening of=20
the northern ridge extension and a realignment of the ridge further east.
This general synoptic progression will lead to increasing mid and=20
upper ascent focused over a large portion of the west coast with
the primary impacts focused over Northern CA up through much of=20
OR/WA state. The beneficiary of the heaviest precip core over the=20
course of D1-2 will be situated within the Cascades with snow levels
hovering between 3000-4000' MSL prior to the stronger height falls
that will occur as the shortwave progresses towards the coast with the
mean trough taking on a more negative tilt as it eventually ejects
inland later this evening. The cold frontal progression associated
with the disturbance will move ashore around the time of the mean=20
trough swinging inland generating a period of falling heights with=20
snow levels dropping closer to 2000-3000' MSL leading to snow=20
accumulations becoming more prevalent in the higher valleys around=20
the Olympic Peninsula and Cascades. Snowfall accumulations of at least
4" remain very high probabilistically (>70%) across the higher=20
elevations of the Cascades and Olympics in WA/OR, as well as the=20
Salmon, Siskiyou and Mount Shasta regions of CA. Mid-level probs=20
between 40-60% for at least 4" are located over the Northern=20
Sierra's with the highest chance in elevations above 7500' MSL.=20

Further inland, the prospects for heavy snow continue later this=20
evening as the shortwave propagates through WA/ID with the greatest=20
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the=20
Interior Northwest with the southern extent benefiting the Absaroka=20
Range of northwest WY. Similar probs of >70% for at least 4" of=20
snowfall exist in those terrain focused regions with the impacts=20
falling within the back-half of D1 into much of D2.=20=20

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly=20
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will=20
maintain onshore moisture advection to support rounds of=20
precipitation into the Northwest, with periodic vorticity lobes=20
swinging eastward (although maintaining latitude generally north of OR)
to enhance ascent. Snow levels D2-3 will fluctuate generally=20
between 2500ft and 4500ft, with rounds of precipitation leading to=20
periods of heavy snowfall. WPC probabilities both D2 and D3 are=20
similar in magnitude and areal extent, reaching 70% or more for 4+=20
inches from the Olympics, to the WA/OR Cascades, eastward through=20
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.=20
2-day snowfall in some of the higher elevations could reach 2-4=20
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...=20
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this=20
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous=20
cases of thundersnow, and prolific snowfall rates of 1-2"/hr=20
beneath the TROWAL over northern Kansas and eastern Nebraska. As=20
the 700mb low traverses northern Missouri this afternoon, a ribbon=20
of 700mb FGEN will pivot and extend over northwest Iowa, southeast=20 Minnesota, and as far north and east as northern Wisconsin.=20
Blizzard conditions will be most common from eastern Nebraska to=20
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"=20
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph=20
are likely in southeast Nebraska and into east-central Kansas. WPC=20
continues to issue Key Messages for the ongoing winter storm and=20
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region=20
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could=20
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine=20
should come to an end Friday night. WPC probabilities shows=20
moderate-to- high chances (40-70%) for snowfall totals >2" in the=20
peaks of the Catskills, Adirondacks, Berkshires, Green, and White=20
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday afternoon.=20

Mullinax




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_0IBMC2Ropaq74jf96TDz8KiNZS996dksNAe42ALwRotb= CnTe2Q1k3T1o6ZgPKkGBMttNVIQ2rq1E0OJeffRufLhCug$=20

$$

=3D =3D =3D
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FOUS11 KWBC 191917
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
317 PM EDT Wed Mar 19 2025

Valid 00Z Thu Mar 20 2025 - 00Z Sun Mar 23 2025


...Pacific and Interior Northwest...=20
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific=20
Northwest and Interior mountains in-of ID/MT/WY over the next 72=20
hrs. Current WV satellite imagery shows a fairly robust upper
trough located off the Pacific Northwest coast with a well-defined
diffluent structure on the eastern flank of the trough axis. The=20
ridge that has been present downstream is beginning to feel the=20
affects of the upstream disturbance leading to some flattening of=20
the northern ridge extension and a realignment of the ridge further
east. This general synoptic progression will lead to increasing=20
mid and upper ascent focused over a large portion of the west coast
with the primary impacts focused over Northern CA up through much=20
of OR/WA state. The beneficiary of the heaviest precip core over=20
the course of D1-2 will be situated within the Cascades with snow
levels hovering between 3000-4000' MSL prior to the stronger=20
height falls that will occur as the shortwave progresses towards the
coast with the mean trough taking on a more negative tilt as it=20
eventually ejects inland later this evening. The cold frontal=20
progression associated with the disturbance will move ashore around
the time of the mean trough swinging inland generating a period of
falling heights with snow levels dropping closer to 2000-3000' MSL
leading to snow accumulations becoming more prevalent in the=20
higher valleys around the Olympic Peninsula and Cascades. Snowfall accumulations of at least 4" remain very high probabilistically=20

70%) across the higher elevations of the Cascades and Olympics in

WA/OR, as well as the Salmon, Siskiyou and Mount Shasta regions of
CA. Mid- level probs between 40-60% for at least 4" are located=20
over the Northern Sierra's with the highest chance in elevations=20
above 7500' MSL.=20

Further inland, the prospects for heavy snow continue later this=20
evening as the shortwave propagates through WA/ID with the greatest
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the
Interior Northwest with the southern extent benefiting the=20
Absaroka Range of northwest WY. Similar probs of >70% for at least
4" of snowfall exist in those terrain focused regions with the=20
impacts falling within the back-half of D1 into much of D2.=20

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly=20
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will=20
maintain onshore moisture advection to support rounds of=20
precipitation into the Northwest, with periodic vorticity lobes=20
swinging eastward (although maintaining latitude generally north of OR)
to enhance ascent. Snow levels D2-3 will fluctuate generally=20
between 2500ft and 4500ft, with rounds of precipitation leading to=20
periods of heavy snowfall. WPC probabilities both D2 and D3 are=20
similar in magnitude and areal extent, reaching 70% or more for 4+=20
inches from the Olympics, to the WA/OR Cascades, eastward through=20
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.=20
2-day snowfall in some of the higher elevations could reach 2-4=20
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...=20
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this=20
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous=20
cases of thundersnow, and prolific snowfall rates of 1-2"/hr=20
beneath the TROWAL over northern Kansas and eastern Nebraska. As=20
the 700mb low traverses northern Missouri this afternoon, a ribbon=20
of 700mb FGEN will pivot and extend over northwest Iowa, southeast=20 Minnesota, and as far north and east as northern Wisconsin.=20
Blizzard conditions will be most common from eastern Nebraska to=20
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"=20
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph=20
are likely in southeast Nebraska and into east-central Kansas. WPC=20
continues to issue Key Messages for the ongoing winter storm and=20
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region=20
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could=20
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine=20
should come to an end Friday night. WPC probabilities shows=20
moderate-to- high chances (40-70%) for snowfall totals >2" in the=20
peaks of the Catskills, Adirondacks, Berkshires, Green, and White=20
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday afternoon.=20

Mullinax





...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4RVlA6qYizTHi3nJ8dq8lnm-w6Igfzgqwy_i_-0FaoL8-= gu5wtaNVq7vc29oqv1khbAzlljoFgcq1NpZg6rlft0iijM$=20

$$

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FOUS11 KWBC 200657
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Thu Mar 20 2025

Valid 12Z Thu Mar 20 2025 - 12Z Sun Mar 23 2025


...Pacific and Interior Northwest...
Days 1-3...

Progressive pattern out of the North Pacific will maintain an
unsettled period for the Pacific Northwest into the northern
Rockies. Initial front has moved past the Cascades as of early this
morning and will continue eastward across the Divide later today.
Next system will be forced by a modestly strong incoming jet
(130kts) tonight with westerly flow focusing into the Cascades,
followed by height falls from the northwest (southwestern Canada)
late Fri into early Sat. That system will dig much farther west out
ahead of incoming ridging into WA/OR, finally setting up some
drier periods on Saturday.

Low snow levels in the Cascades of around 2000-3000ft this morning
will rise through the day and overnight to around 3500-4500ft
(north to south) coincident with the next surge of moisture. Snow
levels will fall again late Fri into early Sat as the Canadian
height falls push into WA then into northern ID, down to around
1500-3000ft from north to south as the precipitation gradually
ends.

Three-day totals of at least 12 inches of snow are likely (>70%
chance) above 3500-4500ft or so from north to south along the
Cascades with some higher elevations receiving more than 2-3 ft.
Significant snow is also possible at many passes given the lower
snow levels. There is a >60% chance of at least 8 inches of snow
above 2500-3000ft or so. Farther east, significant snow in excess
of 12 inches is likely (>70% chance) across the Blue Mountains, central/northern Idaho, northwestern Montana, and into western
Wyoming. The southern extent of the snow will clip northern Utah
and the CO Rockies as well with light/modest amounts near 6 inches
(UT) and nearing 12 inches into CO, especially above 10,000ft.


...Upper Midwest...
Day 3...

The system exiting the High Plains late Sat will continue to dig
into the northern Plains overnight into early Sun. Low pressure
will coalesce over eastern SD Saturday evening and lift into MN
thereafter, bringing WAA-driven snow to northeastern MN, northern
WI, and the western U.P. of Michigan. Amounts will generally be
light through 12Z Sun, perhaps 1-2.5", and the probability of at
least 4 inches is less than 10%. Additional accumulation is likely
beyond this forecast period.


...Great Lakes/Appalachians/Northeast...
Days 1-2...

Exiting system responsible for blizzard conditions over the
central Plains will move into Canada with snow ending over Michigan
this afternoon. Additional snow accumulations will be light (an
inch or so). To the south, colder air will change rain to snow over
the central/southern Appalachians with upslope-driven
accumulations persisting into early Friday. Several inches of snow
are possible at the higher elevations above 3500ft, but WPC
probabilities for at least 4 inches are low (10-40%) along the
TN/NC border. By day 2, low pressure over Cape Cod early Fri will
lift into Nova Scotia with backside snow over northern New England,
but mostly at higher elevations above 2500ft and amounts will
generally be light (<3 inches). The highest peaks of the White
mountains may see more than 4 inches (probabilities generally
10-50%).


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso

$$

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FOUS11 KWBC 201820
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
220 PM EDT Thu Mar 20 2025

Valid 12Z Thu Mar 20 2025 - 12Z Sun Mar 23 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

An active Pacific jet stream pattern will keep periods of mountain
snow in the forecast over the next few days. This is largely due to
a persistent troughing pattern over the Gulf of Alaska that
continues to reload this active pattern with storm systems racing
across the North Pacific that eventually reach the northwestern
U.S.. The Washington Cascades and Olympics above 3,500ft will be
the epicenter for the heaviest snowfall where they are more ideally
placed with the best surge of Pacific moisture, favorable upslope
enhancement, and their placement beneath a strong 130kt 250mb jet
streak aloft. The Oregon Cascades will also be on the receiving
end of accumulating snow, but with higher snow levels farther
south, elevations above 4,500ft will be most favored for heavy
snowfall through Friday. Following a brief break in the active
pattern Saturday morning, an approaching warm front from the next
storm system in line over the Gulf of Alaska will cause noticeably
higher snow levels over the Olympics and Washington Cascades
Saturday night and Sunday. Snow accumulations will likely range
between 1-3 feet in these ranges with some of the tallest peaks of
the Olympics and Washington Cascades topping 4 feet of snowfall
through Sunday.

This same plume of Pacific moisture and the aforementioned jet
streak aloft will advance inland across mountain ranges that
include the Blue, Sawtooth, Bitterroots, Lewis Range, Absaroka, and
Tetons tonight, Friday, and into Saturday morning. Elevations above
5,000ft in the Blue, Sawtooth, Bitterroots, and Lewis Range are
favored to receive as much as 1-2 feet of snow through Saturday
morning. Farther south, elevations above 7,000ft are favored in the
Absaroka and Tetons, as well as other neighboring ranges that
include the Big Snowy, Little Belt, Big Horns, and Bear River
ranges. Snowfall totals of 8-12" will be most common in these
mountain ranges, with the Tetons having better odds of seeing some
snowfall totals topping 2 feet. Lastly, some of this Pacific
moisture will bleed far enough south to reach the Colorado
Rockies and southern Wyoming Rockies Friday night and into
Saturday. Elevations above 9,000ft will be most likely to see
snowfall accumulations >6" with the tallest peaks of the Colorado
Rockies receiving over a foot before the snow tapers off Saturday
night.


...Northern Appalachians & Northeast...
Day 1...

This afternoon, a lobe of 500mb vorticity tracking towards the
Southeast will foster increasing upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region of
a 250mb jet streak, low pressure will organize quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Catskills and Adirondacks on east through the Berkshires,
Green, and White Mountains on Friday. The storm is a quick mover
thanks to the next upper trough within the active jet stream
pattern over the Great Lakes. Any lingering snow in parts of
northern Maine should conclude Friday night. WPC probabilities
depict low-to-moderate chances (20-50%) for snowfall >2" in the
higher elevations of the Green and White Mountains. The tallest
peaks, including Mount Washington, could see some snowfall totals

4" through Friday afternoon.

...Upper Midwest & Great Lakes...
Day 3...

A steepening upper-level trough over the Northern Plains will
provide modest ascent aloft and strengthen low pressure over the
Dakotas. Out ahead of this upper-level trough is increasing
850-700mb WAA that gives rise to low-mid level FGEN over the Upper
Midwest and into the northern Great Lakes Sunday morning. As Sunday
unfolds, a more organized 850mb low is likely to form over
northwest Wisconsin with a much of the atmospheric column well
saturated over northern Minnesota, northern Wisconsin, and the
Michigan U.P.. Based on the track of the 850mb low and the pivoting
deformation axis on the storm's northwest flank, it is northern
Minnesota that presently features the best odds (50-70% moderate
chances) for >4" of snowfall. The Minnesota Arrowhead, with the
added benefit of easterly flow that provides additional lake-
enhancement, has low-to-moderate chances (30-50%) for snowfall
totals >8". Northern Wisconsin and the Michigan U.P. may mix with
rain or stay a wintry mix longer, which combined with generally
lower SLRs may keep snowfall totals a bit more capped compared to
northern Minnesota. However, it will be the CAA on the back side of
the storm and across Lake Superior Sunday night when these areas
see their best chances for measurable snow.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Mullinax




$$

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FOUS11 KWBC 210713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Fri Mar 21 2025

Valid 12Z Fri Mar 21 2025 - 12Z Mon Mar 24 2025

...Northeast...
Day 1...

Low pressure near Cape Cod this morning will move through the Gulf
of Maine and into Nova Scotia this afternoon, helping to draw in
colder air on the back side of the exiting precipitation shield.
Rain will change to snow from west to east with some light
accumulation over most areas, but the higher terrain of the White
Mountains may see a few inches. There, WPC probabilities of at
least 4 inches of snow are 10-40%. In addition, there is a
possibility of some modest snow amounts over eastern Maine outside
the higher terrain as the low deepens in the Gulf of Maine this
afternoon. Snow will end by midnight over eastern Maine.


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Onshore flow continues in the PacNW with a due east jet off the
northeast Pacific aimed into WA/OR. Current jet max along the
Columbia River will continue eastward this morning, but another
will be right on its heels which will promote a moisture plume into
the OR/WA Cascades this afternoon/evening. Snow levels around
3000-5000 ft will still impact the passes today. Snow will lessen
into day 2 (Sat) as height falls dig into the northern Rockies,
which will continue eastward into day 3. By then, upper ridging
will move into the PacNW with a system into the southern AK
Panhandle, allowing snow levels to rise much higher to above 6000ft
Sunday afternoon into early Monday. Three-day totals of at least
12 inches of snow are likely (>70% chance) above 4000ft or so but
primarily on day 1.

West-to-east jet will continue to advance the moisture plume into
the northern Rockies, favoring the Blue, Sawtooth, Bitterroots,
Lewis Range, Absaroka, and Tetons through Saturday morning.
Elevations above 5,000ft in the Blue, Sawtooth, Bitterroots, and
Lewis Range have at least a 70% chance of receiving at least 12
inches of snow through tomorrow morning. Probabilities are a little
lower to the south (Absarokas and Tetons), but many areas will
still see at least 8 inches of snow (>70% chance above 7000ft or
so).

On the south side of the jet and moisture plume, northern UT into
the CO Rockies will likely see at least 8 inches of snow above
9000ft or so (>70% chance), starting later tonight into Saturday
then ending Saturday night.


...Upper Midwest & Great Lakes...
Days 2-3...

Height falls associated with a shortwave exiting Montana Saturday
evening will continue to deepen into MN by Sunday morning in
response to the amplification of the upper pattern upstream. Low
pressure over SD will track eastward into MN with broad WAA ahead
of it over the Upper Midwest. Surface temperatures will be fairly
marginal with some areas starting as rain before mixing with and
changing to snow as the low strengthens on Sunday. As it does,
colder air will wrap around its northwest side over northern MN
moderate snow likely for a time Sunday afternoon. Models have been
wavering on the strength of the upper and sfc features (and thus
the QPF and ultimately the snow), but the eastern Arrowhead (Lake
Shore) may be in a favorable spot for heavier snow due to easterly
flow off Lake Superior. SLRs may start on the lower end below 10:1
then rise as colder air works its way in, but will also combat
afternoon solar insolation where rates are not as heavy. All told,
WPC probabilities for at least 4 inches of snow days 2-3 are at
least 10 percent generally north of I-94, with increasing
probabilities northward and northeastward into the Arrowhead. This
also includes northern WI into the U.P. of Michigan from a
combination of front-end WAA snow and wraparound snow after the low
passes through. Despite likely closing off up to 500mb, the system
will remain progressive but will not clear the area until after
12Z Mon.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


$$

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FOUS11 KWBC 211823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 PM EDT Fri Mar 21 2025

Valid 00Z Sat Mar 22 2025 - 00Z Tue Mar 25 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Onshore flow continues in the PacNW through early next week with
two primary waves of moisture traversing the region with upper
ridging expected to cut off Pacific moisture tap by late D3. For D1
(through 00z Sun), snow levels will drop below 3000 ft across the
Northwest, but also as precipitation quickly dries out and the
focus of upper divergence shifts into the Northern Rockies through
the beginning of D2. Here, snow levels around will start out around
4000-5000 ft but also fall below 3000 ft due to approaching height
falls. By then, upper ridging will move into the PacNW with a
system into the southern AK Panhandle, allowing snow levels to rise
much higher to above 6000ft Sunday afternoon into early Monday as
the next moisture plume clips the Northwest and northern Great
Basin. Totals of at least 12 inches of snow are likely (>70%
chance) above 4000ft or so but primarily on day 1 throughout the
Cascades, Sawtooths, northern ID ranges and western MT ranges, as
well as the Absarokas and Wind River Range of WY. By D2-D3 high
probabilities for at least 6 inches of snow remains confined to the
northern WA Cascades and far northern ID ranges.

On the south side of the jet and moisture plume, northern UT into
the CO Rockies will likely see at least 8 inches of snow above
9000ft or so (>70% chance), starting later tonight into Saturday
then ending Saturday night.


...Upper Midwest & Great Lakes...
Days 2-3...

An upper-level trough exiting the Northern Rockies Saturday
afternoon will track over the Northern Plains and strengthen
Saturday night, providing modest vertical ascent aloft from the
Dakotas to Minnesota. The favorable synoptic-scale source of lift
aloft will provide a favorable environment for a deepening area of
low pressure over South Dakota that will, in turn, generate
increasing 850-700mb WAA in advance of the storm. By Saturday
night, a consolidating 850mb low over the Red River of the North
will wrap modest low-mid level moisture around the northern and
western flanks of the low. As precipitation breaks out from central
North Dakota to as far east as northwest Wisconsin Saturday night,
some precipitation may start out initially as an icy wintry mix.
But as the deformation axis becomes more pronounced, dynamic
cooling aloft will allow for snow to become the primary
precipitation type through Sunday morning. Gusty winds on the
backside of the storm will prompt blowing and rifting snow to ensue
across the Dakota and into northwest Minnesota through Sunday
morning.

The region most likely to witness the heaviest snowfall for this
event is northeast Minnesota or, more specifically, the Minnesota
Arrowhead. The deformation axis is expected to pivot over the
region on Sunday with sufficient vertical velocities throughout
much of the atmospheric column to support heavy snowfall rates

1"/hr, while the Arrowhead, contending with easterlies off of Lake

Superior, provides a lake-enhanced fetch of moisture into the
region Sunday afternoon and into Sunday night. Meanwhile, farther
east, the Michigan U.P., especially the Keweenaw Peninsula on east
to the Hurons and just west of Sault Ste. Marie, the strong WAA
north of the warm front will be sufficient enough to produce a
burst of heavy snow Sunday afternoon and into the evening hours.
This area is a little more unclear on the SLR's and snowfall rates
as there is some evidence of a potential dry slot within the
700-300mb layer working its way in, but there will still be snow to
contend with on the back side of the storm Sunday night. The storm
will work its way over Michigan's U.P. Sunday night with CAA on
the western flank kicking up lake- enhanced snow showers in its
wake across northern Wisconsin and much of the Michigan U.P.. Snow
should finally taper off by Monday afternoon as winds diminish and
lingering lake effect snow showers over the eastern Michigan U.P.
and the tip of Michigan's Mitten wind down.

WPC probabilities show moderate-to-high chances (50-70%) for
snowfall totals >8" along the Minnesota Arrowhead, with similar
probabilities for >6" in northeast Minnesota and in the Michigan
U.P.. Note that there are moderate chances (40-60%) for >4" of
snow as far west as northwest Minnesota and as far south as
northern Wisconsin. Expect hazardous travel conditions in these
areas on Sunday with poor travel conditions lingering over Michigan
U.P.


...Northeast...
Day 3...

As the Upper Midwest and Great Lakes system slides east by D3, a
brief period of moderate snowfall is possible across northern New
England and elevated regions of the Interior Northeast. Mid-level
WAA will be the driving force behind the precipitation pushing
eastward on Monday, with a triple-point surface low developing near
southern New England also providing for potential weak CAD across
parts of ME and NH. WPC probabilities for at least 4 inches of snow
are currently low (10-30%) from the Adirondacks to Green/White Mts
of New England, with slightly higher probabilities in the highest
elevations.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Snell/Mullinax





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FOUS11 KWBC 220720
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Sat Mar 22 2025

Valid 12Z Sat Mar 22 2025 - 12Z Tue Mar 25 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Shortwave over eastern WA this morning will continue east-
southeastward today across the Rockies. Light snow via onshore flow
will continue over the Cascades while light to modest snows are
expected for northwestern MT/northern ID into WY and northern UT/CO
before ending from NW to SE this afternoon and evening. WPC
probabilities for at least 6 inches of additional snow are >50%
above 5000ft (north) to 8000-10,000ft (south). The next system into
the PacNW D2 will be much milder due to increasing mid-level
ridging with snow levels rising from 4000-5000ft late tonight to
over 8000ft Sunday evening. Any initial snow over the passes will
change over to rain with significant snow at the highest peaks. By
D3, upper ridging will remain in control with light snow for the
high elevations as snow levels settle to between 7000-9000ft.


...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

The upper-level trough exiting the Northern Rockies/western High
Plains this afternoon will push into the Upper Midwest tonight into
early Sunday. Multiple vort maxima will lie beneath the poleward
exit region of the modest jet over MO, providing broad vertical
ascent aloft from the Dakotas to Minnesota. Surface low pressure
over South Dakota will deepen and move into MN, with WAA driving
snow (and some mixed precip/light icing) to its northeast (MN into
WI). On Sunday, sharpening upper pattern will and a slight negative
tilt aloft will help increase snow on the NW side of the low in a
modest but still progressive deformation axis. Wraparound snow amid
dynamic cooling and low-level convergence/enhancement on the west
side of Lake Superior will help to maximize snowfall there, from
near/northeast of Duluth northeastward to Grande Portage. A modest
snowfall is expected elsewhere from central MN across northern WI
and into the U.P. of Michigan near and to the north of the track of
the sfc low pressure (and north of any subsequent secondary low
pressure development out of the Corn Belt).

By late Sunday into early Monday, frontal boundary will continue
to arc eastward, pushing precipitation across the Appalachians into northeastern PA and into NYS, where cold surface temperatures may
support some snow and light icing as WAA invades from the
southwest. Limited cold air will confine most snowfall to areas
north of I-90, but with a sfc low track remaining in Canada, many
areas may change over to rain except for northern NH into
northwestern Maine. Back to the west, colder air across the Great
Lakes will spur some lake-effect snow into the U.P. and western
Lower Michigan as 850 temps briefly drop to -10C or so. The entire
system will wind down late Monday with only some lingering lake-
effect snow by early Tuesday.

WPC probabilities for at least 4 inches of snow through the period
are highest (>70%) over northeastern MN and especially over the
eastern Arrowhead (where probabilities for at least 8 inches of
snow are >50%), northern WI and the entire U.P. of Michigan,
northwestern Lower MI, and into the Tug Hill Plateau.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso

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FOUS11 KWBC 221812
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
212 PM EDT Sat Mar 22 2025

Valid 00Z Sun Mar 23 2025 - 00Z Wed Mar 26 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-2...

Shortwave crossing MT/WY this evening will continue areas of high
elevation snow showers and favorable upslope conditions through
early Sunday morning in the Northern/Central Rockies until upper
ridging quickly builds into the West, while directing the next
Atmospheric River event into the Pacific Northwest through D2
(Monday). IVT is forecast to peak on Sunday evening and reach above
the 99th climatological percentile per the 00z NAEFS, with the
maximum corridor of 600-700 kg/m*s IVT directed at WA and the
northern Cascades as moisture also bleeds into northern ID/MT. As
expected, snow levels will quickly rise above 6000 ft and pass
level across the Northwest by D2 after starting out around 3000 ft
for the start of the event. High (>70%) WPC probabilities for at
least 8 inches of snow during the entire forecast period exist
across the WA Cascades and far northern ID/northwest MT ranges,
mainly above 5000-6000 ft.

Snell



...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

An upper-level trough exiting the Northern Rockies this afternoon
will track over Northern Plains and strengthen tonight, providing
modest vertical ascent aloft from the Dakotas to Minnesota. The
favorable synoptic-scale source of lift aloft will provide a
supportive environment for a deepening area of low pressure over
South Dakota. Increasing 850-700mb WAA and moisture advection in
advance of the storm's deepening 850mb will give rise to a
consolidated deformation axis late Sunday night over northern
Minnesota. Precipitation may briefly start out as an icy wintry mix
in parts of the Dakotas and northern Minnesota tonight and early
Sunday morning, but as strong vertical velocities manifest
themselves within the deformation zone, snow will become the
primary precipitation type across northern Minnesota. The heaviest
snowfall is likely to ensue along the Minnesota Arrowhead and
across the northern tier of Michigan's U.P.. Snowfall rates topping
1"/hr are most likely to unfold in these areas Sunday and into
Sunday night. Some of the latest guidance has come a bit farther
south on the storm track (closer to the EC-AIFS/UKMET/CMC solutions
but not completely in their camp), which has led to an increase in
snow over northern Wisconsin. CAA on the backside of the storm
system will keep lake-enhanced snowfall ongoing across northern
Wisconsin and the Michigan U.P. on east to the northern most
portion of Michigan's Mitten through Monday before concluding
Monday evening. WPC probabilities show moderate-to-high chances
(50-70%) for snowfall totals >8" in parts of the Minnesota
Arrowhead and the Michigan U.P.. There are also similar moderate-
to-high chances (50-70%) for snowfall >4" in northern Minnesota,
northern Wisconsin, and the northwestern Michigan Peninsula.

By Sunday night, the storm system's warm front will push into the
Northeast with low-level WAA and 290K isentropic ascent aloft. The
air-mass is marginally cold enough to support snow in the northern
Appalachians Sunday night, with the potential for a burst of heavy
snow in the White Mountains and much of interior Maine on Monday.
Guidance has remained split on whether a coastal low forms along
the Maine coastline, but should it form, locally heavy snowfall
totals (>6") could occur. At the moment, WPC probabilities show
low-to-moderate chances (30-50%) for snowfall totals >4" from the
White Mountains to northern Maine Sunday night and into Monday.
Westerlies over Lake Ontario may kick up a lake effect snow band
that becomes located over the Tug Hill on Tuesday. WPC
probabilities show moderate chances (40-60%) for snowfall totals

4" in the Tug Hill on Tuesday.

For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Mullinax




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FOUS11 KWBC 230705
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Sun Mar 23 2025

Valid 12Z Sun Mar 23 2025 - 12Z Wed Mar 26 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-2...

Upper ridging just off the Pac NW coast this morning will continue
to build into the region, pushing snow levels that are around
3500-5000ft at 12Z to well over 6000-8000ft by 00Z over the
Cascades. Farther east over northern ID into MT, snow levels will
still rise today confining much of the accumulating snow to levels
above 5000ft (>6 inch amounts). Into Monday (D2), moisture will
persist into WA and the northern Rockies but with very high snow
levels above 8000ft. Heights will build into Tuesday, essentially
ending any precipitation in the Northwest altogether.

...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

Mid-level shortwave over the Dakotas this morning will move
eastward today into the Upper Midwest as it surface low pressure
center follows suit across central MN into northern WI. By this
evening, the triple point low will start to become the dominant
center (near Green Bay) and move eastward across northern Lower
Michigan and then into southern Ontario as the cold front bows out
through the Northeast early Monday. With an amplifying upper
pattern, this will slow the progression of the system out of the
region, allowing cyclonic flow to persist over the Great Lakes into
the Northeast into Tuesday, favoring lake-effect snow with 850
temperatures < -10C. Though fairly progressive to start, the system
will still yield significant snow for portions of the eastern
Arrowhead and into the U.P. of Michigan via wraparound/convergent
snow in the deformation band on the NW side of the sfc low, WAA-
driven snow ahead of the sfc low (northern WI into the U.P.), or
both over northern/northwester Lower Michigan via the triple point
low. Over the Northeast, south of the eventual track of the surface
low, WAA will drive much of the precipitation on Monday with some
icing at the onset in colder areas turning over to rain and snow
farther north toward the Canadian border where it will take longer
to warm up toward freezing -- and some areas will not as a result
of a new triple point low over the Gulf of Maine, acting to hold
colder air in over northern NH and northwestern ME. Finally, some
lake effect snow will affect the Tug Hill Plateau Tuesday with
lighter upslope snow to the south into the central Appalachians.
Snowfall will finally wind down by early Wednesday (end of this
forecast period).

For the three-day period, WPC probabilities of at least 4 inches
of snow are highest (>50%) over northeastern MN, northern WI, the
U.P. of Michigan, northern/northwestern Lower MI, and in the Tug
Hill Plateau region including some of the Adirondacks. Some areas
of the White Mountains may see in excess of 4 inches of snow as
well. The heaviest snow may fall over far northeastern MN where
local convergence off Lake Superior will add to the snow efficiency
(in addition to higher SLRs in the colder air). There, WPC
probabilities of at least 8 inches of snow are > 70%.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


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FOUS11 KWBC 231806
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
206 PM EDT Sun Mar 23 2025

Valid 12Z Sun Mar 23 2025 - 12Z Wed Mar 26 2025


...Pacific/Interior Northwest to Northern Rockies...
Day 1...

Ongoing Atmospheric River moving onshore western Washington this
afternoon will continue to spread moisture across the Northwest,
far northern Great Basin and into the northern Rockies through
Monday. Snow levels across the WA Cascades will start out this
evening above 6000 ft and remain between 6000 to 8000 ft throughout
the remainder of the event (above major mountain passes). Snow
levels across the Great Basin and northern Rockies will also
continue to rise above 7000 ft during the D1 period as residual
moisture on the southern edge of the AR reaches into the
western/northern WY ranges. WPC probabilities for at least 6 inches
of snow are medium (30-50%) and are confined to the northern WA
Cascades and highest ranges of MT and WY (above 7000 to 8000 ft).
Precipitation cuts off by D2 as anomalous upper ridging builds
across the western U.S. as the next system approaching the region
cuts off over the northeast Pacific.

Snell


...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

The winter storm has kicked off in the Upper Midwest with the storm strengthening this afternoon as it tracks towards the Upper Great
Lakes tonight. The deformation zone is pivoting beneath the TROWAL
over northern Minnesota. There is also heavy snow unfolding in
northern Wisconsin where strong 850-700mb FGEN and WAA aloft is
paired with dynamic cooling aloft to produce >1"/hr snowfall rates
in some cases. By this evening, the storm will begin its weakening
phase with most snow coming via WAA over the eastern Michigan U.P.
and northern most portion of Michigan's Mitten. Farther west, CAA
on the back side of the low will generate lake-enhanced snowfall
from the Minnesota Arrowhead on east to northern Wisconsin and as
far east as the Keweenaw Peninsula of Michigan's U.P.. Look for
periods of snow lake-effect snow to linger through Monday across
the Michigan U.P. and northern lower Michigan. WPC probabilities
show moderate-to-high chances (50-70%) for additional snowfall
amounts >4" for the areas referenced above, with some localized
areas seeing additional snowfall amounts up to 8", especially in
the Michigan U.P..

Farther east, the storm's warm front will advance east into the
Northeast tonight with low-level WAA and 290K isentropic ascent
aloft. The antecedent air-mass is initially cold enough to support
snow in the as far south as the Poconos and Catskills, but the best
chance for accumulating snowfall will take place over the
Adirondacks, Green, and White Mountains tonight and into Monday
morning. Some minor ice accumulations are possible in parts of the
northern Mid-Atlantic tonight and into early Monday morning. A
wave of low pressure will attempt to develop near Downeast Maine
Monday and could wrap some Atlantic moisture around its northern
and western flank. This would allow for some minor snow
accumulations to unfold from central to eastern Maine through
Monday evening. WPC probabilities do highlight low- to- moderate
chances (20-50%) for some targeted areas of >4" snowfall totals in
parts of the Adirondacks, Green Mountains, White Mountains, and
east-central Maine. As the storm departs Monday night, some lake
effect streamers off Lakes Erie and Ontario should lead to minor
snowfall totals in northwest Pennsylvania, western NY, and northern
New York. The area most likely to see measurable snowfall is the
Tug Hill where the primary band off Lake Ontario and the Tug Hill's
elevation provide a more favorable setup for accumulating
snowfall. WPC probabilities shows low chances (10-30%) for 48-hour
snowfall totals >8" in the Tug Hill, showing there is the potential
for some localized amounts that could be on the heavier side
through Tuesday. Some minor snow accumulations are possible as far
south as the Central Appalachians but totals most totals staying in
the coating-3" range.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Mullinax





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FOUS11 KWBC 240653
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Mon Mar 24 2025

Valid 12Z Mon Mar 24 2025 - 12Z Thu Mar 27 2025


...Pacific/Interior Northwest to Northern Rockies...
Day 1...

Lingering moisture over the Northwest and northern Rockies atop
the upper ridge will slowly dissipate today, with very high snow
levels around 8000ft.


...West Coast...
Day 3...

Next Pacific system will start to bring in some moisture to
western WA/OR and NorCal. Snow levels will still be quite high --
10,000ft on Wednesday -- but dropping to around 5000ft by 12Z
Thursday, which still start to bring snow to some passes.


...Great Lakes/Northeast...
Days 1-2...

Mature winter storm over the Great Lakes this morning will
continue eastward through southern Ontario as a new triple point
low develops near the NY Bight this afternoon. Cold air at the
surface this morning will be slow to erode over the higher
elevations (Catskills, Berkshires/Greens, Worcester Hills, and
parts of Maine) as WAA-driven precip arrives this morning, favoring
some freezing rain amid a snow-to-rain changeover for areas south
of I-90. As the coastal low deepens, it will tend to hold in colder
air over northern New England and much of Maine, with marginal
temperatures toward the coast. This will make for a heavy/wet snow
of a few inches in NH to several inches over interior Maine as the
low pressure moves through the Gulf of Maine this evening. Snow
will end overnight associated with the area of low pressure, but
the large cyclonic circulation over the Great Lakes will sustain
some lake-effect snow today into Tuesday, especially over the
northern U.P. of Michigan, northwestern Lower Michigan, and into
the Tug Hill Plateau. WPC probabilities for at least 4 inches of
snow are >50% over the aforementioned lake-favored areas as well as
over northern NH (White Mountains) into Maine north of I-95 until
Bangor, then along 95 to the Canadian border.


...New England...
Day 3...

Vort max moving through the base of the upper trough over the
Great Lakes on Tuesday will move off the Mid-Atlantic coast and
turn the corner northeastward early Wednesday. Models have wavered
on how close to bring this system to eastern New England, but at
least some light precipitation is likely to affect at least areas
east of I-91. With marginal to somewhat sufficient cold air in
place, some light snow is likely for eastern New England before the
system races northeastward into Atlantic Canada Wednesday evening.
Some of the models were much more vigorous than others, but the
probability of at least 4 inches is still low (10-30%) from
northern NH into Maine.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


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FOUS11 KWBC 241848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EDT Mon Mar 24 2025

Valid 00Z Tue Mar 25 2025 - 00Z Fri Mar 28 2025



...Great Lakes/Northeast...
Days 1-3...

An active later-season winter pattern will setup across the Great
Lakes and Northeast as troughing amplifies over the east and lobes
of vorticity drop southward out of Canada. This will produce
periodic cool and wintry weather across the region.

The period begins active as a wave of low pressure driven by a
strung out vorticity impulse lifts along the coast of Maine. This
system will move quickly into the Canadian Maritimes by 12Z
Tuesday, but a period of moderate to heavy snow is likely to
continue across Maine before this storm pulls away, and WPC
probabilities indicate a medium chance (30-50%) for an additional
2-4" in far northern Maine.

Behind this wave, cyclonic flow will intensify across the Great
Lakes as the resultant trough amplifies down towards the Mid-
Atlantic states. This will drive increasing CAA over the Great
Lakes, with the core of the coldest 850mb temperatures, falling to
as low as -15 to -18 Celsius, moving over the lakes Tuesday night
into Wednesday morning. This cold core combined with unidirectional
flow across the slowly warming lake waters will result in late-
season lake effect snow (LES), especially in the favored WNW snow
belt regions D1 and D2, with upslope snow into Northern New England
also likely D2. *WPC probabilities for this LES are moderate (50%)
for 4+ inches D1 in the eastern U.P., the far northwest L.P., and
across the Tug Hill Plateau. Probabilities for an additional 4+
inches D2 drop to just 10-30% and focus across the Tug Hill
Plateau.

Finally, an interesting development occurs late D2 into D3 as a
potent shortwave tracks over the Mid-Atlantic states, sharpening
the mid-level trough even more, and then lifts northeast off the
New England Coast. This occurs in tandem with a strengthening jet
streak lifting off into Canada leaving the favorable RRQ east of
New England, into which the amplifying trough will deposit the most
robust height falls. The guidance has trended less amplified with
this evolution, but it still supports a surface low developing and strengthening into Wednesday morning. Depending on the exact track
of this low, some moderate snowfall may spread across New England
once again Wednesday night into Thursday, but at this time a more
suppressed solution is more likely, resulting in WPC probabilities
that are 10-30% for 4+ inches of snow from the Northeast Kingdom of
VT, across the White Mountains, and into much of northern and
central Maine.


...West Coast...
Day 3...

Impressive trough amplifying west of British Columbia will deepen
into a closed low as it pivots towards the Pacific Northwest coast
Thursday. The core of this low is progged to become quite
amplified, falling below the 0.5 percentile with respect to 700mb
heights (1st percentile with respect to 500mb heights). This is
indicative of a very strong low which will move eastward, but then
get pulled north within the amplified flow, reaching just off
Vancouver Island by the end of the forecast period.

This evolution will have a two-pronged effect on the West Coast.
First, confluent downstream flow will overlap with an intensifying
Pacific jet streak rotating around the base of this trough to
advect deeper moisture onshore, with both GEFS and ECENS IVT
probabilities reaching above 60% for a narrow corridor of 500
kg/m/s. This moisture will be acted upon by mid-level divergence
and upper diffluence to wring out this moisture through increasing
lift to result in widespread precipitation moving from central CA
northward through the Cascades and Olympics. Additionally, W/SW
mid-level flow will efficiently upslope into the terrain, leading
to locally more impressive lift and heavy precipitation across the
terrain.

Snow levels will initially be quite high, 7000-8000 ft, but will
drop steadily to as low as 3000 ft by the end of the forecast
period behind a cold front working to the east. With this event, a
lot of the precipitation occurs behind the cold front, but still
most of the heavy snow should remain above pass levels. WPC
probabilities are high (>70%) for 6+ inches from the Northern
Sierra, through the Shasta/Trinity/Siskiyou region, along the spine
of the Cascades, and into the higher Olympics. Locally 12+ inches
of snow is possible in the highest terrain,


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Weiss



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FOUS11 KWBC 250644
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Tue Mar 25 2025

Valid 12Z Tue Mar 25 2025 - 12Z Fri Mar 28 2025


...Great Lakes/Northeast...
Days 1-2...

In the wake of the departing system just leaving the Northeast
this morning, broad cyclonic flow centered south of Hudson Bay will
maintain a cold flow of air over the slowly warming Great Lakes,
promoting some lake effect snow for the next couple of days. The
most favored areas will be across portions of the eastern U.P. of
Michigan in any more organized/persistent bands, east of Lake
Ontario along the long fetch of the lake (Tug Hill Plateau), and
into the Green Mountains via upslope enhancement. Two-day totals
will be generally light (1-3") but the aforementioned areas show
the highest probabilities of seeing at least 4 inches of snow
(10-70%, with the highest probabilities of at least 6 inches over
the Tug Hill).


...West Coast...
Days 2-3...

An anomalously deep and impressively wound-up system in the
northeast Pacific late Tue into Wed will start to field moisture
into the West Coast starting Wednesday afternoon. Strong ridging
over the West means snow levels will start very high (>8000ft)
during the middle of day 2 (00Z Thu) but will trend lower into day
3. Then (12Z Thu - 12Z Fri) the upper/sfc low will curl
northeastward to northward to a position just offshore Vancouver
Island, allowing its long occluded front to push inland. This will
take snow levels down to about 5000ft by 12Z Fri over the Cascades
into the far northern NorCal ranges and about 6000-7000ft over the
northern Sierra as a 130kt jet streak moves through. QPF amounts
will be light to modest inland with heavier amounts along the coast
and into the Olympics in WA. Rain will change to snow with low
SLRs and will come in a couple waves -- initially with the front in
the higher PW plume and then with the upper trough. Snow will
accumulate the most at the highest peaks but eventually will get to
some high passes in northern CA. Through 12Z Fri, WPC
probabilities for at least 8 inches of snow are highest (>50%) in
the Olympics, Cascades, and NorCal ranges (Shasta Siskiyous,
Trinity, Klamath, etc.) above 5000ft.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso


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FOUS11 KWBC 252042
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 PM EDT Tue Mar 25 2025

Valid 00Z Wed Mar 26 2025 - 00Z Sat Mar 29 2025


...Eastern Great Lakes/Northeast...
Day 1...

An upper low over northern MI this afternoon shifts east over New
England through Wednesday evening. Low level westerly flow will
continue over the eastern Great Lakes through Wednesday morning
before veering northerly into Wednesday evening. PVA ahead of the
upper low center will aid lift on this favored flow across Lakes
Erie and Ontario and help produce lake enhanced snow and upslope
snow on New England mountain ranges. Day 1.5 snow probs for >4"
are generally 30-50% for the Tug Hill, Greens, Whites, and
northwestern Maine.


...Upper Midwest/Great Lakes...
Day 3...

A flattening upper ridge over the northern Great Plains and lee-
side surface cyclogenesis centered over South Dakota Thursday
night allows some warm air advection precip to form
along and north of the ND/MN border early Friday and possibly blossom
toward Lake Superior later Friday. Antecedent cold air and a warm
nose look to bring a (most likely light) wintry mix to northern
ND/MN/WI and the U.P. Day 3 ice probs for >0.1" are 20-50% centered
around Duluth and up the North Shore.


...Cascades into the northern Sierra Nevada...
Days 2-3...

An anomalously deep, cold core low approaches the OR Coast
Wednesday evening before occluding in place off WA through Friday.
Strong ridging over the West now means high snow levels at onset

8000ft) Wednesday afternoon, but will quickly drop to around

4500ft Wednesday night. These lower snow levels are maintained
through Thursday as the upper low approaches the coast, then drops
even further, to around 4000ft Thursday evening as precip rates
increase again with some heavy rates likely. Day 2 snow probs for

8" are 30-60% for the highest Klamath and OR/WA Cascades only.

However, the lower snow levels and increased precip rates make Day
3 snow probs for >8" more expansive with 40-90% probs from the
northern Sierra Nevada, Klamath, and along the spine of the OR
Cascades and WA Cascades.



Jackson



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FOUS11 KWBC 260636
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Wed Mar 26 2025

Valid 12Z Wed Mar 26 2025 - 12Z Sat Mar 29 2025


...Northeast...
Day 1...

Compact upper low over southwestern Ontario this morning will move
across northern NY/VT midday and through Maine this evening. This
will spur some more light snow into the Tug Hill Plateau where 1-3"
is likely. Farther east, low probabilities (10-30%) are shown for
more than 4 inches of snow over the Green and White mountains via
upslope enhancement as the feature moves through.



...Upper Midwest/Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary astride the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward through Canada and into the Northeast with
an influx of moisture from the southwest, reaching into NY Fri
evening then into New England overnight into early Saturday.
Temperatures are marginal for most areas, confining wintry
precipitation to areas closer to the Canadian border. However, that sub-freezing surface layer will be overrun from the S/SW with
warmer air aloft, promoting a rather large area of sleet/freezing
rain from northern MN eastward across the U.P. of Michigan and
northern WI across Ontario and into the Adirondacks. Ptype from the
models (and NBM) show a strong signal for freezing rain
(impressive for late March), but this may be modulated my afternoon
insolation. Nevertheless, WPC probabilities for at least 0.10"
icing are moderate (30-70%) over northeastern MN, the U.P./northern
WI, and the northern part of Lower Michigan. Snow amounts may be
limited, with the highest amounts of a couple inches over northern
MN where WPC probabilities for at least 4 inches are barely 10%.


...Cascades into the northern Sierra Nevada...
Days 2-3...

An anomalously deep, cold core low in the northeast Pacific will
curl up toward Vancouver Island as its wound up occlude front moves
inland tonight. High snow levels (>8000ft) this afternoon will
steadily drop to around 4000-5000ft tomorrow, then to around 4000ft
Friday with the passage of the upper trough. Snow will eventually
get to some of the passes but much of this will fall over the
higher terrain. Two-day probabilities of at least 8 inches of snow
are highest above 5000ft or so along the Cascades southward to the
NorCal ranges and northern Sierra. Moisture will continue inland to
the northern Rockies with a few to several inches of snow for the
Blue Mountains and into SW MT as a frontal boundary in the area
acts as another focus for forcing. There, WPC probabilities for at
least 8 inches of snow are low (10-30%).


Fracasso


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FOUS11 KWBC 262043
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
443 PM EDT Wed Mar 26 2025

Valid 00Z Thu Mar 27 2025 - 00Z Sun Mar 30 2025


...West Coast through Northern Rockies...
Days 1-3...

An anomalously deep, cold-core low off OR near 140W will further
occlude and curl up toward Vancouver Island through Thursday night
with the occluded front crossing the West Coast tonight. High snow
levels (>8000ft) this afternoon will rapidly drop to around
4000-5000ft after midnight, then to around 3500ft Friday with the
passage of the upper trough axis. Accumulating will eventually
reach to some of the passes in the Cascades by Friday, but the
rates will drop around that time as well. So most of the heavy snow
will be in the higher elevations. Day 2 snow probs for >8" are
50-80% for the higher Cascades, Klamath, and northern Sierra
Nevada.

Moisture will continue inland through the northern Rockies Friday
through Saturday with periodic heavy snow above 5000ft snow levels
on Friday and 4000ft on Saturday. A focus for mountain snow remains
from the Blue Mtns of OR through SW MT (and the Bighorns of WY)
where Day 3 snow probs for >8" are 30-60%.


...Upper Midwest/Northern Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary draped over the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward through southern Canada and the Northeast
with through Friday night. Temperatures are marginal for most
areas, confining snow to areas closer to the Canadian border.
However, a sub-freezing surface layer will be overrun from the
S/SW with warmer air aloft, promoting a long, but narrow swath of sleet/freezing rain from northern MN eastward across the U.P. of
Michigan and northern WI across Ontario, the Adirondacks, and
central New England. Ptype from the models (and NBM) show a strong
signal for freezing rain (impressive for late March), but this may
be initially modulated by Friday afternoon insolation before
focusing over the U.P. of MI Friday evening. Day 2.5 ice
probabilities for >0.25" have risen to 20-40% over much of the U.P.
and the far northern L.P. Day 2.5 snow probs for >4" are 30% up at
the top of the Arrowhead of MN, and 30-70% for Day 3 over the
northern Adirondacks, Greens, and Whites into western Maine.


...Northern Plains...
Day 3...

A shortwave trough axis that crosses the PacNW Friday reaches the
northern Rockies on Saturday promotes Colorado lee-side low
development on Saturday. Broad convergence should allow some
moderate to locally heavy snow bands to form around SD into MN
by Saturday afternoon. The 12Z GFS/EC have come into better
agreement, though the EC remains a bit more progressive. Will need
to monitor the threat for heavy fgen snow banding over portions of
the northern Plains into Upper Midwest Saturday/night.



Jackson


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FOUS11 KWBC 270713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Thu Mar 27 2025

Valid 12Z Thu Mar 27 2025 - 12Z Sun Mar 30 2025


...West Coast through Northern/Central Rockies...
Days 1-3...

An anomalously deep, cold-core low off OR near 135W will further
occlude and curl up toward Vancouver Island through Thursday night
with the occluded front crossing the West Coast this morning. Snow
levels continue to rapidly drop to around 4000-5000ft today across
the Cascades into the northern CA ranges, then to around 3500ft
Friday with the passage of the upper trough axis. Accumulation
will eventually reach to some of the passes in the Cascades by
Friday, but the rates will drop around that time as well. WPC
probabilities for at least 8" of snow are high (>70%) on Days 1-2
across the high elevations of the Cascades and into the northern CA ranges/northern Sierra.

Moisture will continue inland through the northern Rockies Friday
through Saturday with periodic heavy snow above 5000ft snow levels
on Friday and 4000ft on Saturday. Snow also begins to enter the
central Rockies by Saturday as a trailing shortwave crosses the
region and drops snow levels below 7000-8000 ft. Snowfall
probabilities for at least 8" remain greatest across western MT and
towards the Little Belts and Bighorns of WY, where 50-80% values
are found.


...Upper Midwest/Northern Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary draped over the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward from southern Canada and the Northeast
through the daytime on Saturday. Temperatures are marginal for
most areas, confining snow to areas closer to the MN- Canadian
border through Friday and northern NY/VT/NH into ME on Saturday.
However, this band of snow could be quite potent as the region
falls within the right entrance region of a 130 kt jet and IVT over
the 90th climatological percentile over the Great Lakes per the
NAEFS on Friday night. The narrow, but intense WAA combined with
favorable synoptic ascent and moisture could lead to snowfall rates
of 1-2"/hr, particularly across parts of New England by the end of
D2.

Meanwhile, a sub- freezing surface layer will be overrun from the
S/SW with warmer air aloft, promoting a long, but narrow swath of sleet/freezing rain from the northern Plains eastward across the
U.P. of Michigan and northern WI through Ontario, the Adirondacks,
and central New England. Ptype from the models (and NBM) show a
strong signal for freezing rain (impressive for late March), but
this may be initially modulated by Friday afternoon insolation
before focusing over the U.P. of MI Friday evening. Day 2 ice
probabilities for >0.25" have risen to 30-60% over much of the U.P.
and the far northern L.P. Day 2-3 ice probabilities for >0.25"
across the Northeast are 20-40% and highest across the northern
Adirondacks as precipitation lingers through the end of Day 3 while
warmer air begins eventually lifting back north. Day 2 snow probs
for >4" have a very sharp gradient along the MN- Canadian border
with 50-70% values at the top of the Arrowhead of MN. For the
Northeast and New England on Days 2-3, probabilities for >6" have
increased to 30-50% for northern VT/NH and into central ME, with
higher values (60-80%) in the Whites of northern VT and neighboring
areas in ME.


...Northern Plains/Upper Midwest/Northern Great Lakes...
Day 3...

Quickly following the northern Great Lakes system on Day 2 a shortwave
trough axis that crosses the PacNW Friday reaches the northern
Rockies on Saturday along with a southern piece of energy crossing
the central Rockies and promotes Colorado lee- side low
development on Saturday. Broad convergence should allow some
moderate to locally heavy snow bands to form around the Black Hills
of SD (maybe far northern NE) eastward into MN by Saturday
afternoon. The 12Z GFS/EC have come into better agreement, though
the EC remains a bit farther north with the axis of heavier snow.
WPC probabilities for at least 4" of snow are 30-50% from northern
WI to the western U.P., with lower probabilities (10-30%) extending
from the Black Hills of SD through central MN. These probabilities
are likely to increase over the next few forecast cycles once
better agreement in the northern extent of QPF comes into focus. With
high pressure remaining locked in over the southern Hudson Bay,
there remains a strong signal for mixed ptype from MN through WI
and into the U.P. and northern L.P. of MI. Day 3 freezing rain
probabilities for >0.25" are currently low (10-30%) from central WI
through the northern L.P. of MI.



Snell


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FOUS11 KWBC 272037
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
437 PM EDT Thu Mar 27 2025

Valid 12Z Thu Mar 27 2025 - 12Z Sun Mar 30 2025


...West Coast through Northern/Central Rockies...
Days 1-3...

A deep, slow-moving low centered off of the Northwest coast will
gradually fill as it lifts to the north over the next couple of
days. However, even as the system lifts out, snow levels across the
Northwest will continue to drop Friday into early Saturday as a
series of shortwave troughs digging south of the low move inland.
This will bring levels down to around 3000-4000ft in the Washington
and Oregon Cascades on Friday, before dropping below 3000ft with
the passage of a well-defined trough Saturday morning. Further to
the south, snow levels starting above 5000ft in the Shasta-
Siskiyou region and the northern Sierra Nevada will drop below
4000ft in many locations before precipitation ends. Although snow
levels will be on the decline, so will the onshore moisture
advection, with guidance showing IVTs dropping off after the start
of the period. The heaviest precipitation is expected to center
across southern Oregon and far northern California, where the best
moisture and forcing is expected to focus later today. By early
Saturday, precipitation is expected to diminish from south to north
as an upper ridge moves inland in the wake of the previously-noted
trough. Probabilities for 72-hr accumulations exceeding 8in are
over 50 percent for parts of the Olympics, Cascades, Klamath
Mountains, and the northern Sierra Nevada.

Meanwhile, moisture spreading inland will begin to interact with a
developing low-to-mid level baroclinic zone and periods of
enhanced forcing associated with the inland moving troughs to
produce light-to-moderate precipitation, including mountain snow
from the northern to the central Rockies. Precipitation coverage is
expected to increase Friday night, with unsettled weather
continuing through the weekend. Snow levels beginning above 5000ft
in the northern Rockies Friday night are forecast to dip below
4000ft in some location by late Saturday. In the central Rockies,
snow levels will drop to 7000-8000ft in the Colorado ranges and
around 5000-6000ft across northern Utah. Probabilities for 72-hr
accumulations exceeding 8in are above 50 percent across portions of
the northern and central Rockies from western Montana to
northwestern and north-central Wyoming and from south-central
Wyoming to north-central Colorado.

...Northern High Plains and Black Hills...
Days 2/3...

A shortwave trough moving into the Southwest on Friday is expected
to lift northeast from the Four Corners across the central Rockies
and into the High Plains Saturday morning. Moisture fed into an
area of strong ascent generated in part by favorable upper jet
forcing will support precipitation north of an associated surface
low that will develop and move east of the Colorado Rockies. Rain
changing to snow is expected from southweastern Montana and
northeastern Wyoming into parts of western to central South Dakota
and Nebraska. The heaviest amounts are forecast to fall across the
Black Hills, where totals exceeding 4in are likely.

...Upper Midwest/Northern Great Lakes/Northeast...
Days 1-3...

A longwave upper trough in the West working in tandem with the
right-entrance region of a 250mb jet streak Friday afternoon will
foster large-scale ascent aloft throughout the Upper Midwest and
Great Lakes. The upper trough and a strong low-level ridge of high
pressure off the Southeast coast supports a strengthening SWrly
low-mid level flow regime that results in exceptional warm-air
advection (WAA) for the regions reference above. The WAA from the
Upper Midwest and Great Lakes to interior New England will clash
with a cold Canadian air-mass anchored by a 1030mb+ high pressure
system over Ontario and Quebec. The result is 925-700mb FGEN that
produces a narrow band of disruptive snow and ice starting Friday
afternoon from northern Minnesota to the Upper Great Lakes,
followed by interior New England's start time of Friday night. The
strong WAA over sub- freezing boundary layer temps is a favorable
setup for freezing rain/sleet that will make for hazardous travel
conditions.

By Saturday morning, a brief break in the action arrives from
northern Minnesota to the Upper Great Lakes, but periods of
mountain snow and valley ice will linger throughout much of the day
in New England. WPC probabilities for this event show moderate
chance probabilities (40-60%) for >0.25" of ice accumulation over
the tip of Michigan's Mitten and the far east section of Michigan's
U.P.. Some instances of scatter power outages and tree damage
cannot be ruled out here. Meanwhile, there is an expansive area of
moderate- to-high chance probabilities (50-70%) for >0.1" of ice
from northeast Michigan, northern Wisconsin, and for the rest of
northern Michigan. Snow will be the primary hazard Friday night and
into Saturday morning over interior New England. WPC probabilities
show moderate-to-high chances (50-70%) for snowfall totals >4"
from northern Vermont (excluding the Champlain Valley) on east
through northern New Hampshire and west-central Maine. The peaks
of the White Mountains could see snowfall totals top 8". WSSI-P
does show some moderate chances (40-60%) for Minor Impacts in these
affected areas of Interior New England.

This active pattern reloads over the Central Plains on Saturday as
the longwave trough in the West ejects a shortwave disturbance
over the Rockies. This feature will spawn a new wave of low
pressure along the 925-850mb front that remains stationary from
Nebraska and southern Minnesota on east through Michigan. There
remains some discrepancies in guidance on the evolution/strength of
this storm system. The ECMWF SATs MSLP guidance shows the low
organizing over eastern Kansas that heads into eastern Iowa by
Sunday morning. Ultimately, the 290K isentropic ascent and strong
WAA mechanisms that supported the first round of wintry weather
will still be present Saturday night and into Sunday from the
Midwest to New England. The ECMWF-AIFS does show the potential for
a deformation zone on the backside of the storm over eastern South
Dakota and into central Minnesota, although thermodynamic profiles
are not sold yet on which areas can dynamically cool enough to stay
all snow. There is higher confidence in yet more freezing
rain/sleet from northern and central Wisconsin on east through
northern Michigan and as far east as northern New England. WPC
probabilities show moderate chances (40-60%) for ice accumulations

0.1" in these areas with low chances (10-30%) for >0.25",

especially in the more elevated terrain. In terms of snowfall, WPC probabilities show low-to-moderate chances (30-50%) for snowfall
totals >4" in far northern Wisconsin and the western Michigan U.P..

Pereira/Mullinax


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FOUS11 KWBC 280748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Fri Mar 28 2025

Valid 12Z Fri Mar 28 2025 - 12Z Mon Mar 31 2025


...West Coast through Northern/Central Rockies...
Days 1-3...

A deep, slow-moving low centered off of the Northwest coast will
gradually fill as it lifts to the north over the next day or so.
However, even as the system lifts out, snow levels across the
Northwest will continue to drop into early Saturday as a series of
shortwave troughs digging south of the low move inland. This will
bring levels down to around 3000-4000ft in the Washington and
Oregon Cascades today, before dropping below 3000ft with the
passage of a well-defined trough Saturday morning. Further to the
south, snow levels starting above 5000ft in the Shasta- Siskiyou
region and the northern Sierra Nevada will drop below 4000ft in
many locations before precipitation ends. Although snow levels will
be on the decline, so will the onshore moisture advection, with
guidance showing IVTs dropping off after the start of the period
and a break in precipitation on Day 2. The heaviest precipitation
is expected to center across southern Oregon and far northern
California, where the best moisture and forcing is expected to
focus later today. By early Saturday, precipitation is expected to
diminish from south to north as an upper ridge moves inland in the
wake of the previously-noted trough. Day 1 WPC probabilities for
over 8 inches of snow are 60-80% for parts of the Olympics,
Cascades, Klamath Mountains, and the northern Sierra Nevada. Then,
the next system approaches the West Coast by Day 3 as the closed
upper low off the Pacific Northwest reloads from energy dropping
southward across the eastern Aleutians. This leads to additional
moderate onshore flow amid initial snow levels around 4000-5000ft
(up to 6000ft in the central/southern Sierra). WPC probabilities
for at least 8 inches of additional snow on Day 3 across the Sierra
and northern CA ranges are 40-70%, but are expected to increase as
the bulk of the precipitation moves onshore after 12z/Mon.

Meanwhile, moisture spreading inland across the northern Great
Basin and Rockies will begin to interact with a developing low-to-
mid level baroclinic zone and periods of enhanced forcing
associated with the inland moving troughs to produce light-to-
moderate precipitation, including mountain snow from the northern
to the central Rockies. Precipitation coverage is expected to
increase Friday night, with unsettled weather continuing through
the weekend and ending with a weak area of convergence on Sunday
between western MT and northern CO. Snow levels beginning above
5000ft in the northern Rockies Friday night are forecast to dip
below 4000ft in some location by late Saturday. In the central
Rockies, snow levels will drop to 7000-8000ft in the Colorado
ranges and around 5000-6000ft across northern Utah. WPC Days 1-2
probabilities for at least 8 inches of snow are generally 50-70%
from the Blue Mts of northwest OR through the central ID ranges
into southwest MT, as well as the Absarokas and Wind River Range.
These probs also extend south to the Park Range and Medicine Bow
Mountains of CO/WY.


...Northern Minnesota through the Northern Great Lakes...
Day 1...

A longwave upper trough in the West working in tandem with the
right-entrance region of a 250mb jet streak this afternoon will
foster large-scale ascent aloft throughout the Upper Midwest and
Great Lakes. The upper trough and a strong low-level ridge of high
pressure off the Southeast coast supports a strengthening SWrly
low-mid level flow regime that results in exceptional warm-air
advection (WAA) for the regions reference above. This WAA will
clash with a cold Canadian air-mass anchored by a 1030mb+ high
pressure system over Ontario and Quebec. The result is 925-700mb
FGEN that produces a narrow band of disruptive snow (primarily
north of the U.S.-Canadian border) and ice starting as early as
this morning across far northern MN, but becoming more widespread
across northern MN/WI/MI by this evening. The strong WAA over sub-
freezing boundary layer temps is a favorable setup for freezing
rain/sleet that will make for hazardous travel conditions even
where only light amounts occur. WPC probabilities for at least
0.25" of ice accretion on Day 1 is medium (50-70%) across the
eastern U.P. and northern L.P. of MI, with 20-40% chances extending
westward across the U.P. and into the MN Arrowhead.


...Northeast...
Days 1-3...

This same system is expected to spread a narrow swath of heavy snow
and area of mixed precipitation into the Interior Northeast and New
England by late D1, but with wintry precipitation lingering for
several days. This long-duration event made possible by a trailing
shortwave and developing central U.S. trough which will continue to
reinforce a favorable jet pattern for upper divergence as well as
sufficient mid-upper level moisture content. However, the snowfall
threat peaks early Saturday morning as a jet max passes to the
north of New England and 925-850mb WAA is at it's strongest. 00z
HREF depicts 30-40% chances for 1-2"/hr snowfall rates around
13z/Sat across far northern NY and northern VT/NH. WPC snowfall
probabilities for at least 6 inches of snow on days 1-2 are medium
(40-60%) from northern NH, VT, and into central ME.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition area of sleet/freezing rain. After the brief
burst of heavier precip early Sat, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to a
strong 1030mb High situated over the James Bay. This potentially
significant icing threat is expected to linger through Sun morning
until the surface low across the Midwest begins to strengthen and
push warmer air northward across New England by Day 3. However, the
CAD signature in place will continue to support freezing rain
across the typically colder valley locations and areas banked along
the Green/White mountains. WPC probabilities for the entire
forecast period (ending 12z/Mon) are high (70-80%) for at least
0.25" of ice accretion from the NY border with eastern Ontario
through the northern Adirondacks and into central VT/NH.
Probabilities for at least 0.5" also impressive and 40-60% (highest
across western Jefferson county of NY).


...Northern High Plains through the Upper Midwest/Great Lakes...
Days 2-3...

A shortwave trough moving into the Southwest today is expected to
lift northeast from the Four Corners across the central Rockies and
into the High Plains Saturday morning. Moisture fed into an area
of strong ascent generated in part by favorable upper jet forcing
and potent 700mb closed low will support precipitation north of an
associated surface low that will develop and move east of the
Colorado Rockies. Rain changing to snow is expected from
southeastern Montana and northeastern Wyoming into parts of
western to central SD and NE. The highest amounts are forecast to
fall across the Black Hills, but locally heavy totals are also
possible eastward along southern SD and north- central NE. WPC
probabilities for at least 4 inches are 40-70% across the Black
Hills and 10-30% into south-central SD and north- central NE.

As this system develops further Saturday night through Day 3,
increasing WAA and a blossoming precipitation shield is expected to
spread into the Upper Midwest and Great Lakes. Surface low pressure
is expected to track along along the 925-850mb front that remains
stationary from NE and southern MN on east through Michigan. There
still remains some discrepancies in guidance on the evolution/strength
of this storm system, but there is a growing consensus with the
00z guidance on the synoptic scale. The GFS finally has a more
amplified solution (in line with the CMC and ECMWF), which paints
an axis of snow fall extending east-northeast from SD through
central MN into northern WI and the MI U.P.. There is also higher
confidence in yet more freezing rain/sleet from northern and
central WI on east through northern Michigan as high pressure
remains locked in place over James Bay and cold northeast flow
continues to filter into the Upper Midwest/Great Lakes. This is a
very favorable setup for potentially significant freezing rain from
northern WI through northern MI, especially for late-March. WPC
probabilities show moderate chances (30-60%) for ice accumulations

0.25" in these areas with low chances (10-30%) for >0.5" across

parts of northern WI. In terms of snowfall, WPC probabilities show
moderate chances (30-60%) for snowfall totals >6" in far northern
WI and the western MI U.P..

Snell





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FOUS11 KWBC 282111
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
511 PM EDT Fri Mar 28 2025

Valid 00Z Sat Mar 29 2025 - 00Z Tue Apr 01 2025


...Northern/Central Rockies...
Days 1/2...

A shortwave trough ejecting from the remnant/occluded low off WA
crosses the PacNW tonight and the Great Basin through Saturday
night. This maintains moisture spreading across the northern Great
Basin and Rockies will begin to interact with a developing low-to-
mid level baroclinic zone and periods of enhanced forcing
associated with the inland moving troughs to produce light-to-
moderate precipitation, including mountain snow from the northern
to the central Rockies. Precipitation coverage is expected to
increase tonight, with unsettled weather continuing into Sunday
with a weak area of convergence on Sunday between western MT and
northern CO. Snow levels beginning above 5000ft in the northern
Rockies are forecast to dip below 4000ft in some location by late
Saturday. In the central Rockies, snow levels will drop to
7000-8000ft in the Colorado ranges and around 5000-6000ft across
northern Utah. WPC Day 2 probabilities for >8" of snow are
generally 40-70% over southwest MT, the Absarokas and Wind River
Range, and the Park Range and Medicine Bow Mountains of northern CO.


...South Dakota, Minnesota, and Northern Wisconsin/Michigan...
Days 1/2...

...Back to back impactful winter systems through Sunday...

Inverted trough from central High Plains up through lower MI
persists tonight as an upper low approaching the northern Rockies
this afternoon allows lee-side cyclogenesis to focus over western
KS through Saturday morning with a more potent low track from KS to
MI Saturday through Sunday evening.

A very strong baroclinic zone (it's currently low 80s in southwest
MN and mid 20s in the Arrowhead) maintains cold over northern
MN/WI/the U.P. through this weekend while warm air rides over the
boundary to the south. Ongoing wintry mix continues tonight with a
slow southward shift. Day 1 ice probs for >0.1" additional after
00Z is about 20% over far northern WI into the western U.P., but
50-80% over far northeast WI and central/eastern U.P. and northern
L.P. with 70% probs for >0.25" over the northern L.P.

The developing low track over KS on Saturday allows
fgen/deformation banding to develop over over southwest SD into
northwest Neb. Localized banding should overcome the strong March
diurnal insolation, but that should be fairly narrow. Day 1.5 snow
probs for >4" are 30-60% mainly over south-central SD and the Black
Hills.

The impactful wintry weather continues resumes Saturday night over
MN/WI/MI as snow bands intensify in the increasing right entrance
jet dynamics and the comma head forcing from the low tracking over
IA. These snow bands are increasingly likely over north-central MN,
far northern WI and western/central U.P. which would put heavy wet
snow over areas currently getting ice accretion. Day 2 snow probs
for >4" are 30-60% from the Sisseton Hills of northeast SD through
the central U.P. and North Shore of MN with 50-70% probs for >6"
over far northern WI through the Keweenaw Peninsula. The wintry mix
swath is just south of the snow with accumulating sleet and ice
expected to expand south as the cold air wins/advances. Day 2 ice
probs for >0.25" are 30-70% from central MN through northern WI/southern/eastern U.P. and the northern L.P. with a max around
80% in northeast WI.


...Northeast...
Days 1-3...

...Prolonged wintry mix over northern NY/New England through
Sunday...

The inverted trough causing a wintry mix over the northern Great
Lakes today spreads east over northern NY and central New England
this evening with the strong baroclinic zone maintaining fgen
precip/wintry mix through this weekend for portions of New
England. The approaching low crosses New England on Monday.

The heavy snowfall threat peaks late tonight from Lake Champlain
through northern NH into southern Maine as a jet max passes to the
north of New England and 925-850mb WAA is strongest. 12Z HREF
depicts 30-40% chances for 1"/hr snowfall rates from 06Z to 13Z
Saturday across the northern tip of NY and northern VT/NH. Day 1
WPC snowfall probabilities for >6" are 30-60% mainly over the
northern Greens and the Presidential Range of NH.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition zone of sleet/freezing rain. After the brief
burst of heavier precip early Sat, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to a
strong 1030mb High situated over the James Bay. This potentially
significant icing threat is expected to linger through Sunday until
the surface low across the Midwest begins to strengthen and push
warmer air northward across New England by Sunday evening.
However, the CAD signature in place will continue to support
freezing rain across the typically colder valley locations and
areas banked along the Green/White mountains. Day 1 WPC
probabilities for >0.25" ice (ending 00Z/Sun) are 40-70% for the
Thousand Islands area, the northern Adirondacks and south-central
VT/NH. This is followed by Day 2 values of 20-50% for an additional
0.25" over the same areas with some expansion through central
VT/NH.


...OR Cascades...Klamath...and northern/central Sierra Nevada...
Day 3...


The next cold core low drifts toward OR, but remains offshore
Sunday through Monday. A rich plume of moisture shifts inland
Sunday with renewed enhancement from an ejecting shortwave trough
Sunday night producing heavy precip over the northern half of CA
Monday. Day 3 snow probs for >8" are 40-90% in the southern OR
Cascades, the Klamath/Trinity Alps, and northern/central Sierra
Nevada with snow levels of 5000-6000ft Sunday dropping to
4000-5000ft by Monday morning.




Jackson



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FOUS11 KWBC 290823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Sat Mar 29 2025

Valid 12Z Sat Mar 29 2025 - 12Z Tue Apr 01 2025


...Central/Northern Plains, Upper Midwest, and Northern Great
Lakes...
Days 1-2...

Long-duration ice storm to impact northern WI through the northern
MI L.P. and much of the central/eastern U.P. through Sunday, while
moderate to heavy snow is likely from SD/Neb through far northern
WI and along the lakeshore of Lake Superior.

A negatively tilted upper trough will cross the Intermountain West
today and usher potent SWrly flow into the north-central U.S.,
while a leading mid-level shortwave ejects into the central Plains
by this afternoon. This leading shortwave is associated with
leeside cyclogenesis along the CO/KS border and an attached sharp
stationary front extending east-northeast through the Midwest and
Great Lakes. As moisture overruns this frontal boundary and
expansive high pressure stretches across Canada, a wintry mix of
snow, sleet, and freezing rain is likely this weekend.

Snowfall is forecast to begin across western Neb into the Black
Hills and south-central SD by this afternoon associated with the
mid-level low crossing overhead leading to sufficient convergence
and bands of snowfall capable of containing 1-2"/hr rates. These
rates will be imperative to achieving heavy accumulations as
boundary layer temperatures start out well above freezing. The 00z
HREF depicts the best chances for these intense snowfall rates are
along the western and central SD/Neb border centered near the Pine
Ridge Reservation. Snowfall rates will likely lower while the
northern precipitation shield expands east-northeast in response to
the progressing surface low and forcing becoming more stretched in
an east-west direction. Moderate snow will extend across SD,
central MN, and towards far northern WI and the MI U.P. by tonight.
There has been some latitudinal uncertainty regarding this swath
of snow, with 00z guidance coming in a touch south. Regardless, WPC probabilities for at least 4" of snow are 30-60% for this region,
with localized pockets up to 80%. Meanwhile, the heaviest snowfall
from this system is most likely from near or just south of Duluth,
MN eastward along the lakeshore of Lake Superior from far northern
WI into the MI U.P. due to snow remaining the dominant ptype
throughout the event. Here, WPC probabilities for at least 6" are
high (60-80%).

South of the heavy snow axis a corridor of impactful sleet and
freezing rain are forecast to stretch from northern WI through much
of northern MI. A prior storm has already led to a corridor of ice
across this region and precipitation may linger continuously today
across northern WI/MI until a resurgence tonight through Sunday.
High pressure (~1030mb) over James Bay will continue to usher in
cold northeasterly flow as the surface low tracks across southern
WI on Sunday. Ice accretion may be limited during daytime hours
given the late-March sun angle, but with the bulk of the wintry mix
occurring Saturday night there is the potential for significant
ice accumulations. WPC probabilities for at least 0.25" of freezing
rain are highest (60-90%) across parts of northern WI and the
northern MI L.P., with chances for >0.5" at 30-60%. Medium
probabilities (30-60%) for at least 0.25" also extend into the
central/eastern MI U.P. as well as into parts of northwestern WI to
the border of MN. In addition to the freezing rain threat, some
areas from northern WI to the MI U.P. could experience over 1" of
sleet.


...Northeast...
Days 1-2...

Prolonged wintry mix expected across the Interior Northeast through
New England this weekend, including the potential for heavy icing
before above freezing temperatures return on Monday.

An initial pulse of heavy precipitation is swinging through
northern NY and New England this morning, including heavy snow up
to 1"/hr until around 14Z across northern VT into central/northern
NH. This snowfall is a result of a jet max passing to the north of
New England and where 925-850mb WAA is strongest, which quickly
wanes later today.

South of this heavy snow threat between the northern Adirondacks
and much of central/southern VT and NH, 850-750mb warm nose allows
for a transition zone of sleet/freezing rain. After the brief
burst of heavier precip this morning, forcing weakens and there is
left a weak stream of moisture overrunning a CAD signature due to
the strong High situated over the James Bay and elevated PWs (above
the 90th climatological percentile per the NAEFS SAT) continuously
advected from the WSW. WAA gains latitude by Sunday as the Great
Lakes low pressure strengthens and tracks northeast into Canada by
Sunday night. Even with this storm track turning the entire northeast eventually over to rain on Monday, a prolonged wintry mix this
weekend could lead to significant freezing rain amounts. Areas most
at risk for heavy icing include northern NY and the Adirondacks,
through the Greens and Whites of VT/NH, where CAD is likely to
remain longest.

WPC probabilities for >0.25" ice are 60-80% for the Thousand
Islands area, the northern Adirondacks and south- central VT/NH.
Probabilities for >0.1" ice extend as far south as the MA
Berkshires and northward along the White Mts through ME into Day 2.


...Northern/Central Rockies...
Days 1-3...

An upper trough sliding eastward across the Intermountain West
today will maintain some Pacific moisture advection into the
northern/central Rockies while also interacting with a developing
low- to- mid level baroclinic zone to produce light-to- moderate
mountain snow this weekend. Precipitation coverage is expected to
peak on Day 1 as the upper trough moves through, with unsettled
weather continuing through Sunday across MT/WY due to the
relatively strong baroclinic zone being reinforced by high
pressure positions over southern Saskatchewan. Snow levels
beginning around 5000ft in the northern Rockies are forecast to dip
below 4000ft in some location by this evening. In the central
Rockies, snow levels will drop to 7000-8000ft in the Colorado
ranges and around 5000-6000ft across northern Utah. WPC Days 1-2
probabilities for >8" of snow are generally 40-70% over southwest
MT, the Absarokas and Wind River Range, and the Park Range and
Medicine Bow Mountains of northern CO.

By the end of Day 3/12z Tuesday, a strong closed upper low returns
to off the Pacific Northwest and extends a 160kt 250mb westerly
jet inland through the central Great Basin. Pacific moisture,
upslope flow, and increasing upper divergence to the north of this
low produces the next round of mountain snow across the
northern/central Rockies. Current WPC Day 3 probabilities for at
least 8" are 30-50% from southwest MT, western WY, into the
northern CO Rockies.


...West Coast through the Intermountain West...
Days 2-3...

The next cold core low drifts toward OR, but remains offshore
Sunday through Monday. A broad plume of Pacific moisture shifts
inland Sunday and lifts northeastward with renewed enhancement
from an ejecting shortwave trough Sunday night producing heavy
precip over the northern half of CA Monday. Days 2-3 snow probs for

8" are 50-90% in the southern OR Cascades, the Klamath/Trinity

Alps, and northern/central Sierra Nevada with snow levels of
5000-6000ft Sunday dropping to 4000-5000ft by Monday morning. Snow
also extends into the central/northern Great Basin Sunday night
through Monday, with snow levels falling below 4000-5000ft on Day 3
across the Idaho ranges and remaining around 5000-6000ft across
UT/NV.


Snell



$$

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