Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
205 PM EST Tue Feb 25 2025

Valid 00Z Wed Feb 26 2025 - 00Z Sat Mar 01 2025

...Pacific Northwest through the Northern Rockies...
Day 1...

Potent surface low moving ashore far northwest WA along with a
weakening upper low opening into an upper shortwave over the
Northern Rockies tonight will continue to produce areas of heavy
snow through early Wednesday. The atmospheric river once associated
with this system will end by this evening as IVT values drop to
below 250 kg/m*s once upper ridging builds along the West Coast.
However, lingering precipitation is expected across the northern
WA Cascades and northern ID/western MT ranges overnight, including
the Bitterroots and Lewis Range, especially above 3000-3500 ft. In
these areas, WPC probabilities for an additional 6+ inches of snow
are high (>70%), and pass level impacts will continue until snow
wanes during the middle of D1.


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

A modest wave of low pressure will move northeast from the Great
Lakes across New England Thursday into Friday, with an accompanying
cold front trailing in its wake. The low will likely track across
central New England, with the accompanying WAA causing
precipitation to expand in the form of snow across northern New
England. Although the system will be fast moving, brief heavy snow
is likely in the higher terrain of the White Mountains of NH where
WPC probabilities reach 30-50% for 4+ inches of accumulations.
There is a chance for some light ice accumulations (<0.1")
associated
with the WAA across the Catskills, Adirondacks, and Berkshires on
Thursday, but with the surface low crossing to the west there
won't be much time for ice to accrete after the mid-level warm
nose changes ptype to rain. By D3, as a secondary cold front passes
to the east, post- frontal upslope flow will develop into the
Adirondacks and northern Greens, with modest lake enhancement
occurring into the Tug Hill Plateau. In these areas, WPC
probabilities for 4+ inches reach 50-70%, but with higher values
(70-90%) across the Tug Hill.


...Upper Great Lakes...
Day 3...

By Thursday night into Friday morning, a clipper system diving
southeast across south-central Canada will begin to spread a swath
of WAA driven snow into far northern MN. This system will progress
eastward quickly with snowfall spreading across the majority of
the Upper Great Lakes on Friday, including northern WI, the MI
U.P. and northern L.P. There remains some north-south uncertainty
with GFS/GEFS depicting a more southerly solution and heavy (4+
inches) amounts extending across the MN Arrowhead through northern
MI, while the ECMWF/ECENS depicts the heaviest snow confined to
the eastern U.P. The GFS is likely on the southern end of the
guidance due to a slightly more amped downstream 500 mb pattern
ahead of the clipper system. Current day shift forecast fell in
between, while leaning towards the northern ECENS solution. WPC
probabilities are largely 20-40% across the region for 4+ inches of
snow on D3, with 40-60% chances across the eastern U.P. of MI.


Snell/Weiss