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

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


...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
agreed upon by all guidance; a strong jet streak over northern
Mexico will place its highly divergent left-exit region over the
central Plains Monday night. Paired with strong PVA ahead of the
500mb low in the Rockies aloft will organize and strengthen a
surface low in lee of the Colorado Rockies as early as Monday
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
through 12Z Wednesday as the storm moves into the Midwest.
Interestingly, NAEFS/ECWMF SATs depict mean IVT surpassing the

97.5th climatological percentile over eastern CO early Tuesday

morning. This is a byproduct of the exceptional 500-700mb moisture
aloft that is associated with the deformation axis producing a
burst of heavy snow. This will focus the heaviest snow along the
Palmer Divide and southeast Front Range of southeast WY via strong
enough NErly upslope flow, along with stronger dynamic cooling
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
Divide for snow and wind gusts, suggesting the potential for
significant impacts via those to weather hazards. Through 00Z
Wednesday, WPC probabilities show moderate-to-high chances
(40-70%) for snowfall >6" along the Palmer Divide and the Front
Range of southeast WY.

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

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
Mississippi Valley. Periods of heavy snow and whiteout conditions
are likely in these areas with heavy snow even stretching into the
Michigan U.P.. From Minnesota on east to northern Wisconsin and
the Michigan U.P., these areas are more at risk for heavy snow
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
moderate-to-high chances (40-70%) for snowfall >6" from southeast
MN to northern Wisconsin and the central Michigan U.P.. The ECMWF
EFI depicts >0.8 values for heavy snow and wind gusts in these
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
Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

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