FOUS11 KWBC 040832
QPFHSD

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

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

...Pacific Northwest through the Central Rockies...
Days 1-3...

An active pattern, driven by an impressive northeast Pacific
longwave trough, will deliver a steady diet of rich Pacific
moisture into the Pacific Northwest and Northern Rockies. ECMWF
SATs for 06Z Wednesday show 1000-700mb heights that are below the
0.5 climatological percentile and a strong atmospheric river that
is headlined by a >1,250 kg/m/s IVT. Even as this atmospheric river
(AR) wains Wednesday evening and another moderate AR arrives on
Thursday, from a winter perspective, the strong 850-500mb WAA and a
lack of sufficiently cold air-masses will keep accumulating
snowfall limited to the more remote areas of the Cascades and
Northern Rockies. While some lingering Pacific moisture streaming
across these mountain ranges on Day 1, the ARs on Days 2 and 3 will
produce the bulk of the heavy mountain snow. Cumulatively over the
next 3 days, WPC probabilities >50% for snowfall >8" are most
commonly seen above 5,000ft in the WA Cascades, above 7,000ft in
the Sawtooth and Lewis Ranges, and above 9,000t in the Absaroka,
Tetons, and Wind River Ranges. Passes not yet closed for the
season in these ranges could contend with hazardous travel
conditions.

...Northern New England and the Adirondacks...
Day 2...

By Wednesday morning, an amplifying upper level trough over the
Great Lakes will deepen a wave of low pressure tracking through
southern Ontario Wednesday afternoon, culminating in a potent sub-990mb
low over the Gulf of Maine early Thursday morning. Precipitation
will overtake much of northern NY and northern New England by
Wednesday evening first via 850-700mb FGEN and associated WAA
within that atmospheric layer. Given the lack of a sufficiently
cold antecedent air-mass, any periods of snow will likely be
confined to the tallest peaks of the Adirondacks, Green and White
Mountains, and western Maine. It is not until the storm heads for
coastal Maine, when low-level CAA ensues and NWrly flow increase
favorable upslope ascent into these mountain ranges that leads to
snow levels plummeting to as low as 500-1,000ft throughout northern
NY and northern New England. It is a fast moving storm system, and
the time roughly between 03-09Z Thursday is when the heaviest
snowfall rates are likely to occur. No long after 12Z Thursday,
only lingering upslope flow into the >2,000ft ranges of the
Adirondacks, Green, and White Mountains are likely to see any
lingering snowfall.

WPC probabilities shows moderate-to-high chances (40-70%) for
snowfall >4" in western ME, northern NH, and the White Mountains
(including most notably Mount Washington). The peaks of the Green
Mountains and Adirondacks generally have low chances (10-30%) for
totals >4", with their tallest peaks having the best chances for
>4" totals. Impacts, such as snow-covered roads and reduced
visibility, will generally be confined to more remote locations of
these areas.

The probability of significant ice across the CONUS is less than
10 percent.

Mullinax
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