FOUS11 KWBC 210619
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
219 AM EDT Wed Oct 21 2026

Valid 12Z Wed Oct 21 2026 - 12Z Sat Oct 24 2026

...Southern Sierra Nevada...
Days 1-2...

The closed upper-low off the Southern CA coast will direct a plume
of tropical moisture at the Southwest U.S. today and into Thursday.
Some of this moisture source will be directed at the southern
Sierra Nevada where a combination of topographically-induced
upslope flow and synoptic scale support in the form of a 120kt+ 
250mb jet streak will aid in enhanced precipitation rates and 
mountain snow. Latest 00Z HREF/REFS probabilistic guidance shows 
low-to-moderate chances (30-50%) for >1"/hr snowfall rates 
Wednesday night and into Thursday morning. These snowfall rates 
will be observed higher up in the southern Sierra Nevada with most 
areas above 9,000ft witnessing these potential snowfall rates. Snow
is expected to taper off Thursday night. The Probabilistic 
Precipitation Portal (PPP) does show moderate-to-high chances 
(50-80%) for snowfall totals >6" above 9,000ft in elevation, with 
low chances (10-30%) for snowfall amounts exceeding 12" above 
11,000ft. The WSSI shows Minor Impacts are anticipated for 
elevations at/above 9,000ft, indicating winter driving conditions 
are expected and to exercise caution when driving in at those 
elevations.

...Central Rockies...
Days 2-3...

The same closed low responsible for the heavy snow in the Sierra
Nevada will work in tandem with upper-level ridging over the
South Central U.S. to project an impressive IVT into the
Intermountain West. By 18Z Thursday, the IVT is surpassing 500
kg/m/s in eastern AZ and eastern UT, which is surpassing the
maximum observed values in the CFSR climatology (1979-2009). This
highly anomalous moisture transport will upslope into various 
mountain ranges throughout the Intermountain West (San Juan, NV 
Great Basin ridge, Wasatch, Wind River, Tetons, Absaroka). Most 
accumulations will be on the minor side given the lack of a 
sufficiently cold air-mass. Thursday is the snowier day for the San
Juan Mountains, while Friday is the snowier day for the mountains 
ranges across UT, NV, ID, southwest MT, and western WY.

Latest PPP shows low-to-moderate chances (30-50%) for snowfall 
totals >6" in the more remote elevations of the San Juan, Teton, 
Wind River, and Absaroka Ranges. Localized snowfall amounts 
approaching 12" in the peaks on the San Juan Mountains are 
possible, especially where hourly snowfall rates >1"/hr occur. The
WSSI-P shows <20% odds for Moderate Impacts throughout the 
Intermountain West. Some travel disruptions at pass levels are 
possible given the moderate-to-high chances (50-80%) for Minor 
Impacts in parts of the San Juan, Tetons, and Absaroka most 
notably. 


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


Mullinax





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