Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
222 AM EST Sun Nov 1 2026

Valid 12Z Sun Nov 01 2026 - 12Z Wed Nov 04 2026

...Sierra Nevada into the Intermountain West & Rockies...
Days 1-2...

An increasingly amplified mid-level pattern across the western and
central CONUS will bring widespread unsettled weather from the
Desert Southwest, through the Intermountain West, and into the High
Plains over the next few days. High elevation impactful snowfall
is likely across the higher terrain, with periods of lesser lower-
elevation snows also possible.

An impressive full latitude trough will be moving inland along the
West Coast to begin the period, and this trough will gradually
translate eastward into the Great Basin before closing off Sunday
evening. This trough will continue to push to the east through
early this week, with precipitation ending across the Rockies
Tuesday morning.

While most of the precipitation is expected to be rain, heavy
mountain snow is likely, especially above 9000 ft. The primary
mechanism for this is downstream advection of impressive IVT
exceeding 500 kg/m/s surging from the tropical Pacific and as far
east as the Central Plains. This intense moist advection, reflected
by NAEFS ensemble PW above anything previously measured for this
timeframe in the CFSR database, will further expand heavy
precipitation across a large portion of the region. Coverage and
intensity of this precipitation is expected to peak this afternoon
through early Monday morning across the Southwest, Central Great
Basin, and Rockies. However, the accompanying WAA will also keep
snow levels elevated as noted above, limiting significant
accumulations to above 9000 ft across the Sierra, Unitas, San
Juans, higher CO Rockies, Sawtooth, and Wind Rivers. However, in
these areas, snow will be impactful due to low SLR leading to
moderate to locally major (major in the San Juans) impacts from
snow load forecast via the WSSI-P.

The heaviest additional accumulations are likely in the San
Juans, Uintas, Wind River Range, and CO Elk Mts, where there is a
greater than 50% chance for at least 12 inches of snow, with
locally 2 feet storm total possible. Farther north, the higher
elevations of the Big Horns also have a 50% chance for at least 8
inches of snow. While most of the snow should remain at the highest
elevations, as the low wraps up and some cold air pulls into the
system within increasing deformation across MT/WY Sunday night
through Monday night some lower elevation mixing may occur, but
notable accumulations below 6000 ft are not currently expected.


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


Weiss/Snell