FOUS11 KWBC 130745
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Mon Oct 13 2025

Valid 12Z Mon Oct 13 2025 - 12Z Thu Oct 16 2025

...California & Central Nevada...
Days 1-2...

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

An upper low dropping southward along the West Coast is forecast
to deepen into a robust 500mb closed low off the California coast
by Monday night before swinging inland across central California on
Tuesday and eventually the central Great Basin on Wednesday. This
rapid amplification of the 500mb closed low (18Z ECMWF shows 500mb
heights below the 0.5 climatological percentile and nearing October
records off the California coast Tuesday morning) 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 today and continuing through early
Wednesday, with snow levels remaining around 7,000ft to start in
the southern Sierra within the more robust precipitation axis. A
healthy IVT topping 400 kg/m/s is helping to direct a rich plume of
Pacific moisture at the mountain ranges. However, recent model
trends over the last 24 hrs have indicated a slightly further south
location of the upper- low, which lowers the QPF somewhat across
the central Sierra due to less orthogonal (more southerly) flow
into the Sierra Nevada terrain. This produces better upslope flow
into the southern CA ranges (ptype primarily rain) and southern
Sierra Nevada versus the prior forecasts centered on the central
Sierra. Regardless, snow still arrives over the northern California
mountains today with the heaviest snowfall occurring late tonight
into Tuesday over the central/southern Sierra Nevada. Given the
lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra. 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 southern/central Sierra Nevada Monday night
into Tuesday. Look for some heavy snowfall to spill into central
Nevada's taller ranges with anywhere from 12-24" of snowfall
possible over 8,000ft.

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 up to 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 Major to Extreme Impacts, which would imply dangerous
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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