FOUS11 KWBC 290730
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 AM EDT Tue Oct 29 2024

Valid 12Z Tue Oct 29 2024 - 12Z Fri Nov 01 2024


...Central Rockies onto High Plains....
Day 1...

Widespread mountain snow, with locally heavy amounts, is expected
as a well-defined shortwave moving through the base of a broader-scale
trough lifts northeast from the Southwest, crossing the central
Rockies into the High Plains over the next 12 hours. Areas likely
impacted will extend from the southern Utah and southwestern
Colorado mountains to the Wyoming ranges and the Black Hills.
Strong upward ascent afforded in part by a developing upper jet
couplet and low-to-mid level frontogenesis, will generate moderate
to heavy snow that will translate northeastward across the region
today. HREF guidance indicates that locally intense bands,
producing rates of 1-2 in/hr, can be expected to develop initially
over the Utah and western Colorado mountains this morning before
lifting into Wyoming, where more widespread heavy snow is likely
to develop by the afternoon and continue into the evening. WPC
guidance shows locally high probabilities for accumulations of 8
inches or more along the central Utah and west-central Colorado
ranges. More widespread coverage is shown across the central
Wyoming ranges, including the Wind River and eastern Absaroka
ranges, the Owl Creek Mountains, and Big Horns. WPC guidance
suggests widespread amounts of 8 inches or more across these areas,
with totals topping 18 inches across some of the higher terrain.
Rain changing to snow will produce some lighter accumulations,
generally around 1-2 inches across the northeastern Wyoming Plains.
However, heavier accumulations of 8 inches or more can be expected
across the higher elevations of the Black Hills.

...Northwest to the Northern Rockies...
Days 2/3...

Much of the Northwest will be dry today as a shortwave ridge
builds and moves east across the region ahead of the next
approaching system. This next system will be a deep low that is
expected to rapidly develop over the Gulf of Alaska today. This
system is forecast to drop south, with its associated frontal band
expected to move into the Pacific Northwest on Wednesday. As the
low reaches the Northwest on Thursday, it is forecast to turn to
the east and move toward the northern Rockies as it gradually
weakens. The heaviest precipitation is expected to focus across
western Oregon and northwestern California, generated by strong
forcing and moisture advection. Significant snow accumulations are
likely along the Oregon passes as snow levels dip below 4500 ft. By
Wednesday night, snow will begin to develop and spread east from
the northeastern Oregon into the central Idaho ranges, where some
locally heavy amounts of 6 inches or more can be expected by Friday
morning.

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


Pereira


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