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FOUS11 KWBC 121913
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Sun Oct 12 2025

Valid 00Z Mon Oct 13 2025 - 00Z Thu Oct 16 2025

...Northern Rockies & Pacific Northwest...
Days 1-2...

Snow has subsided in parts of WY and central ID as the 500mb
shortwave trough responsible for snowfall late yesterday and
overnight tracks into south-central Canada. However, periods of
moderate-to-heavy snow will linger over western MT as cold
Canadian high pressure nosing southward allows for favorable
upslope ascent in this region, with general low-to-mid level
convergence extending across northern WA and ID along a sinking
frontal boundary. This will favor light to moderate snow across
areas above 5,000ft, but with snow levels dropping enough for minor
accumulations for parts of the MT Front Range and adjacent High
Plains above 4,000ft through tonight. For the Cascades of WA and
OR, snowfall will be tied to the amplifying upper low emerging from
British Columbia as snow levels start around 4,000-5,000ft (lowest
in the northern WA Cascades) before eventually lowering to around
3,000ft in WA and 4,500ft in OR on Monday

WPC probabilities show moderate-to-high probabilities (50-80%) for
storm-total snowfall amounts >8" from the Cascades on eastward into
the northern ID Panhandle to the Lewis Range of MT. Over western
MT and the ID Panhandle, including Glacier Nat`l Park, an
additional... particularly above 7,000ft. The WSSI shows mostly
Minor Impacts, signaling potentially slick travel conditions, while
some passes in MT and Glacier Nat`l Park may contend with Moderate
Impacts that could result in road closures.

...California & Central Nevada...
Days 2-3...

...First significant snowfall event of the season set to impact
the Sierra Nevada beginning Monday night...

The upper low dropping southward along the West Coast is forecast
to deepen into a robust 500mb low off the California coast. This
amplification of the 500mb trough (06Z ECMWF shows 500mb heights
below the 0.5 climatological percentile and nearing October records
off the California coast Monday afternoon) is due to an impressive
anti-cyclonic wave break over British Columbia. Height falls and
modest 500-700mb CAA aloft will support lowering snow levels down
to around 6000-6500ft through the Siskiyou and the Sierra Nevada
starting Monday and continuing through the first half of next week.
A healthy IVT topping 400 kg/m/s is helping to direct a rich plume
of Pacific moisture at the mountain ranges. Snow arrives over the
northern California mountains on Monday with the heaviest snowfall
occurring Monday night into Tuesday over the Sierra Nevada. Given
the lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra Nevada. This raises concerns for
potential impacts to trees and infrastructure given this is the
first significant mountain snowfall in the Sierra Nevada this
season. WPC`s Snowband Probability Tracker shows HREF guidance
identifying 2-3"/hr rates over the central Sierra Nevada Monday
night. Look for some heavy snowfall to spill into central Nevada`s
taller ranges with anywhere from 6-12" of snowfall possible.

WPC probabilities show moderate-to-high chances (50-80%) for at
least 24" of snowfall throughout the central Sierra Nevada (above
8,000 feet) through Wednesday with maximum amounts exceeding 36"
possible. Latest WSSI-P shows moderate-to-high chances (50-80%)
for Major 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. Current WSSI also
highlights Moderate to Major Impacts, which would imply difficult
to impossible travel at times between Monday night and much of the
day on Tuesday, including for many major passes.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax/Snell






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