Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
214 PM EDT Sat Oct 31 2026

Valid 00Z Sun Nov 01 2026 - 00Z Wed Nov 04 2026

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

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. 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 deepening off the
Pacific Coast to being to 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
into the middle of next week, but there is greater-than-typical
uncertainty with the evolution and phasing of multiple mid-level
impulses across the Central/Northern Plains by Tuesday.

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 expand heavy precipitation
across a large portion of the region. However, the accompanying WAA
will 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 accumulations are likely in the Sierra, San Juans, and
Uintas, where there is a greater than 90% chance for at least 12
inches of snow, with locally 2 feet possible. Farther north, the
higher elevations of the Big Horns and Wind Rivers and Sawtooth
have a 60% chance for at least 12 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