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. 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
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), 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.
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, 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
(20-50% chance of at least moderate impacts due to snow load from
the WSSI-P.
The probability of significant ice across the CONUS is less than 10
percent.
Weiss
The whole discussion, as WPC wrote it
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
210 PM EDT Thu Oct 29 2026
Valid 00Z Fri Oct 30 2026 - 00Z Mon Nov 02 2026
...Sierra Nevada into the Intermountain West & Four Corners...
Day 2-3...
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. 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
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), 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.
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, 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
(20-50% chance of at least moderate impacts due to snow load from
the WSSI-P.
The probability of significant ice across the CONUS is less than 10
percent.
Weiss
