FOUS11 KWBC 111834
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Sat Oct 11 2025
Valid 00Z Sun Oct 12 2025 - 00Z Wed Oct 15 2025
...Northern Rockies...
Days 1-2...
A potent shortwave upper-level trough tracking through the Pacific
Northwest will generate healthy vertical ascent over the Northern
Rockies that combined with sufficient moisture aloft and falling
heights will prompt the development of moderate-to-heavy mountain
snow over the Northern Rockies starting this evening and lingering
into Sunday. As heights steadily fall and precipitation rates
increase Saturday night into Sunday morning, snow levels will drop
to as low as 4,000ft across far northwest MT but the heavier
snowfall totals (>6") will be most commonly found above 5,000ft
along the Lewis Range, including Glacier Nat'l Park. Accumulating
snowfall will extend as far west as the Blue and Sawtooth Mountains
and as far south as the Teton and Wind River Ranges of western
Wyoming through Sunday morning. Snow will stick around through
Sunday night over the Lewis Range and on the eastern foothills of
central Montana thanks to a dome of Canadian high pressure
fostering upsloping easterly flow that prolongs the heavy snowfall
into Monday morning.
WPC probabilities show moderate-to-high probabilities (50-80%) for
storm-total snowfall amounts >8" from the Idaho Panhandle on east
to the Lewis Range. Mountains within and around Glacier Nat'l Park
even have moderate chances (40-60%) for over 12" of snow,
particularly above 7,000ft. Farther south into the Absaroka,
Teton, and Wind River Ranges, WPC probabilities show high chances
70%) for snowfall totals >4" above 8,000ft. Expect lighter
snowfall totals (1-4" on average, locally higher in taller peaks)
in parts of the Bitterroots, Sawtooth, and Blue Mountains. The WSSI
shows mostly Minor Impacts due to potentially slick travel
conditions, while some passes in Montana and Glacier Nat'l Park may
contend with Moderate Impacts that could result in road closures.
...Pacific Northwest & Sierra Nevada...
Days 2-3...
Farther west, as the Northern Rockies upper-level disturbance exits
north and east, another 500mb trough will strengthen and dive south
through the Pacific Northwest late Sunday and eventually deepen to
a robust 500mb low off the northern California coast by Monday
afternoon. This sudden amplification of the 500mb trough (06Z ECMWF
shows 500mb heights below the 1st climatological percentile off
the California coast Monday afternoon) is due to an impressive
anti-cyclonic weak break over British Columbia. The dramatic
height falls and modest 500-700mb CAA aloft will support lowering snow
levels along the Cascades, Olympics, and on south through the
Siskiyou and the Sierra Nevada starting Sunday and continuing into
the first half of next week. All guidance also shows a healthy IVT
topping 400 kg/m/s helping to direct plenty of Pacific moisture at
the mountain ranges. The heaviest snowfall in the Pacific Northwest
unfolds late Sunday morning and into Sunday night before gradually
tapering off by Monday morning. Monday is when snow arrives over
the northern California mountains with the heaviest snowfall
occurring Monday night into Tuesday over the Sierra Nevada.
Guidance has come in snowier over the past 12-24 hours, and given
the lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra Nevada. This could raise concerns for
potential impacts to trees and infrastructure given this is the
first significant mountain snowfall in the Sierra Nevada this
season.
WPC probabilities show minor accumulations (less than 4") as low
as 4,000ft in elevation over the Cascades and Olympics, but
elevations at and above 4,000ft sport high chances (>70%) for
snowfall totals >4" through the first half of next week. Some
peaks above 6,000ft in western OR and western WA could see
snowfall totals top 12" in spots. In California, the northern
Sierra Nevada above 7,000ft and the central Sierra Nevada above
8,000ft have moderate-to-high chances (50-80%) for >12" of
snowfall and low-to-moderate chances (30-50%) for amounts >18"
through Tuesday afternoon. Latest WSSI-P shows moderate chances
(40-60%) for Moderate Impacts along the central Sierra Nevada with
the Snow Amount, Snow Load, and Snow Rate impacts being the main
concerns for the first significant snow of the season.
The probability of significant freezing rain across CONUS is less
than 10 percent.
Mullinax
$$
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