FOUS11 KWBC 280750
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 AM EDT Mon Oct 28 2024

Valid 12Z Mon Oct 28 2024 - 12Z Thu Oct 31 2024


...Western U.S....
Days 1-3...

An amplified upper trough moving across the western U.S. is
forecast to produce widespread mountain snow from the Pacific
Northwest and the Sierra Nevada to the northern and central
Rockies. Areas of heavy accumulations are expected, especially for
portions of the central Rockies on Tuesday.

A well-defined shortwave moving through the base of the upper
trough is expected to lift northeast from the Southwest through the
central Rockies on Tuesday. In addition to strong mid-to-upper
level forcing, upslope flow on the northwest side of an associated
low level wave moving across Wyoming, will likely support periods
of heavy snowfall along the favored terrain. Ranges that will be
impacted include the Wind River, southern Absaroka, and the Big
Horns. WPC probabilities are 50 percent or greater for
accumulations of 8 inches or more across parts of these areas.
Locally heavy snows are also likely in the Black Hills, with
amounts of 6 inches or more likely, according to WPC probabilities.

As the system lifts out of the Southwest, other areas impacted
will include the southwestern and west-central Colorado ranges,
including the San Juan and Elk mountains, where heavy heavy snows
are forecast to begin tonight, with storm totals, according to WPC
probabilities, likely reaching over a foot before snow diminishes
on Wednesday. Further west, widespread mountain snows are expected
along the Utah mountains as well, from the southern mountains to
the Uintas, with WPC probabilities indicating that locally heavy
amounts of 8 inches or more likely.

In the Northwest, onshore flow along the backside of the trough,
will continue to support unsettled weather across the region
through today. Snow levels will remain low enough to support light
accumulations along the higher Cascades passes. Snow is expected to
diminish on Tuesday as a shortwave ridge builds ahead of the next
approaching system. Precipitation will then return by late
Wednesday with the arrival of a frontal band associated with a deep
upper low dropping south from the Gulf of Alaska. This will bring
the return of mountain snow to the Olympics and the Cascades and
the potential for impacts across the higher Cascades passes.

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

Pereira


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