Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 PM EST Sat Mar 1 2025

Valid 00Z Sun Mar 02 2025 - 00Z Wed Mar 05 2025


...Great Lakes & Northeast...
Day 1...

Strong surface low pressure system exiting northern New England
this evening will continue to usher potent CAA behind an arctic
cold front clearing the East Coast tonight. Outside of lingering
wrap-around snow across northern Maine, heavy accumulating
snowfall through Sunday will be confined to localized lake-effect
bands. With 20-35 kt 850 mb winds out of the northwest, the best
chances for additional moderate snowfall is across the eastern MI
U.P. and areas southeast of Lake Ontario. Here, WPC probabilities
are low (10-30%) for an additional 4"+ of snow.


...California & Great Basin...
Days 1-2...

A closed upper-low tracking into California on Sunday will direct
IVT
topping out around 250 kg/m/s at the 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 Sunday afternoon and into Sunday night. As the
upper low approaches Sunday night, 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 night and into
Monday. Moisture and a potent upper low will then eventually reach
the Central Rockies late 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.


...Northern & Central Rockies to the Central Plains...
Day 3...

The upper low responsible for the mountain snow in the highly
elevated ranges of California and the Great Basin will make its
way into the Central Rockies on Monday and eventually the Central
Plains on Tuesday. Falling heights 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.

There remains a fair amount of spread regarding the snow potential
in the Central and Northern Plains. The synoptic-scale jet stream
setup is generally agreed upon; a strong jet streak over northern
Mexico will place its divergent left-exit region over the central
Plains Monday night. Along with strong PVA ahead of the 500mb low
in the Rockies will result in rapid cyclogenesis in lee of the
Colorado Rockies that will organize and strengthen a surface low by
Tuesday. Where guidance differs are on the storm track, the rate
at which the storm deepens, and the extent to which the colder air
to the north is in place soon enough to result in a swath of heavy
snow in the Northern Plains. Today's guidance is starting to come
into better agreement with a dynamically colder band of
precipitation breaking out across the central High Plains Tuesday
morning, but with above average spread remaining on exact
placement. The GEFS members remain generally little faster and
therefor deeper/north with the storm by 00Z Wednesday compared to
the ECENS which is slower and farther south. This leads to some
differences regarding the location and magnitude of a potential
swath of snow on D3 extending from eastern Colorado through the
central Plains into eastern North Dakota. The one thing these
ensembles have in common is focusing on the Palmer Divide and
southeast WY with strong enough NErly upslope flow, along with
stronger dynamic cooling aloft to support heavier snowfall.
Interestingly, NAEFS mean IVT reaches >97.5th climatological
percentile even though flow is out of the north. However, any
faster storm motion could mean less snowfall, and the opposite for
heavier snow should the storm slow down. Through 00Z Wednesday, WPC
probabilities show moderate chances (40-60%) for snowfall >6"
along the Palmer Divide and parts of southeast Wyoming, with lesser
chances for >4" (10-30%) over parts of western Nebraska and south-
central South Dakota.

With a lack of sufficiently cold air east of the Rockies, snowfall
potential will be more directly tied to the deformation axis
placement and dynamic cooling aloft from the Denver metro on north
and east. Given the potentially record-strong low pressure over the
Midwest by Tuesday night, greater impacts could be related to
strong winds. Residents in the Central and Northern Plains will
want to monitor the forecast closely over the weekend as this is a
complex storm system.


Snell/Mullinax