Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Thu Nov 20 2025

Valid 12Z Thu Nov 20 2025 - 12Z Sun Nov 23 2025

...Southern & Central Rockies...
Day 1...

An upper low over AZ this morning will take on an increasingly
negative tilt over northern Mexico though weaken overnight as it
mostly shears out to the east after 00Z. Snow will continue this
morning over northern AZ/NM into UT/CO with relatively high snow
levels >8000ft that will drop through the day. Some light snow will
still persist into D2 (early Friday) as lingering convergence and
upslope squeeze out another inch or two over the CO Rockies. WPC
probabilities for at least four inches of snow after 12Z Thu are
highest (>50%) over the highest peaks of the San Juans and the
Sangre de Cristos (generally above 10,000ft).

...California...
Days 1-2...

A Pacific upper low will form early this morning just west of
WA/OR and dive south-southeastward today through NorCal then to a
position west of Los Angeles early Friday. With regions of
vorticity rotating around the main center, bouts of snow will move
through the CA terrain from the Trinity/Siskiyou mountains today
then through the Sierra later this afternoon into Friday. Snow
levels will be around 5000-6000ft this morning over NorCal and
around 6000ft over the central/southern Sierra this evening and
slowly drop overnight. Over SoCal, snow levels will be around
6500ft this afternoon and drop to around 6000ft overnight. The
upper low will be in no hurry to exit the region, moving through
northern Baja California Saturday evening. By then, most of the
precipitation will be confined to the lower elevations and mostly
rain (though snow may linger over the SoCal mountains).

WPC probabilities for at least six inches of snow are >50% above
about 9000ft over the Sierra. Across the San Gabriel and San
Bernadino mountains, with a longer duration of precipitation
through Friday, significant snowfall is quite probable. WPC
probabilities for at least eight inches of snow are >50% above
about 7000ft (around the elevation of Big Bear Lake). Three-day
totals may exceed 12-18" above 9000ft. This could cause significant
travel disruptions over these higher elevations.

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

Fracasso