FOUS11 KWBC 300639
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
239 AM EDT Fri Oct 30 2026

Valid 12Z Fri Oct 30 2026 - 12Z Mon Nov 02 2026

...Sierra Nevada into the Intermountain West & Four Corners...
Days 1-3...

An impressive full-latitude upper trough, represented by NAEFS
height anomalies falling below the 10th percentile along most of
the Pacific Coast, will gradually pivot eastward into early next
week over the Intermountain West and Rockies. Downstream of this 
deepening trough, a subtropical jet streak will amplify and surge 
northeast, with downstream diffluence overlapping with intensifying
mid-level divergence to produce robust deep layer ascent across 
the Southwest and Intermountain West this weekend. 

Moisture embedded within a pronounced IVT plume (peak IVT above 500
kg/m/s from the West-WRF centered over the Southwest) will lift
into the increasing ascent, resulting in widespread precipitation,
most prominent on D2 and D3, from southern CA through the Northern
Rockies. The WAA accompanying the IVT will push snow levels to 
9000-10000 ft across the Intermountain West (slightly lower-8000 
ft in ID/MT and higher-11000 ft in CO), keeping most of the 
precipitation rain. However, accumulating snow is likely in the 
higher elevations, with periodic lowering of snow levels to 
7000-9000 ft (near the NBM 10th percentile, varying with location) 
thanks to steep lapse rates aloft and some enhanced ascent through 
700-600mb fgen and upslope forcing. As the pronounced trough 
crosses over the Rockies by the end of D3, snow levels will 
gradually fall below 7000-8000ft across the Northern Rockies and 
Great Basin, but coinciding with drying northwesterly mid-upper- 
level flow early Monday.

Some light snow is possible D1, but in general accumulating snow
will occur primarily on D2 and D3. During this time, the higher
elevations of the Sierra will be favored for the heaviest
accumulation, with a 60% chance of at least 12 inches, with local
maxima approaching 2 feet. Additional heavy snow exceeding 6 inches
is likely (>60%) across the higher elevations of the Sawtooth of 
ID, the Uintas of UT, Wind River Range of WY, and the San Juans of
CO, where locally 12+" is possible. All of this snow will likely 
be comprised of less- than-climatological SLR, leading to 
substantial snow load impacts (50-90% chances of at least moderate 
impacts due to snow load from the WSSI-P across the San Juans).


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


Weiss/Snell



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