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FOUS11 KWBC 021920
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Sat Nov 2 2024

Valid 00Z Sun Nov 03 2024 - 00Z Wed Nov 06 2024

...Mountainous West... 
Days 1-3...

A series of upper level disturbances will carve out a longwave
trough across Intermountain West this weekend, with another
imposing shortwave trough hot on its heels that arrives in the
Pacific Northwest to kickoff the first full week of November.
Numerous mountain ranges across the West, including but are not 
limited to: Cascades, Blue, Northern Rockies, Tetons, Wind River, 
Uinta, and Wasatch, can expect periods of snow this evening that
linger into Sunday morning. As a trailing shortwave trough over the
northern Great Basin dives southeast Sunday morning, 500mb and
700mb height falls will ensue across the Four Corners states. Snow
will pick up in intensity along the Wasatch Sunday morning, the
over the southern Wyoming and central Colorado Rockies Sunday
afternoon. Snowfall rates will increase along the Front Range of
the Colorado Rockies Sunday afternoon and evening as low pressure
strengthens over the eastern Colorado High Plains and a favorable
combination of low level upsloping northeasterly flow combined with
strong upper level divergence ahead of the trough sets up over
central Colorado. This will likely result in not only heavy snow
as far south as the Sangre de Cristo and Raton Pass, but minor 
snow accumulations along the Palmer Divide and portions of the 
Denver/Boulder metro area Monday morning. Snow will linger in parts
of the southern Rockies through early afternoon, then come to an 
end by Monday evening. WPC PWPF shows moderate-to-high chances 
(50-70%) for >8" of snowfall in parts of the Wasatch and central 
Rockies above 9,000ft. There are similar probabilities for parts of
the Sangre De Cristo and Raton Pass through Monday morning.

In the Pacific Northwest, a brief break in the active pattern
arrives Sunday night and into early Monday morning, but the next
northeast Pacific storm system arrives late Monday morning and will
bring another round of heavy snow to the Washington Cascades. NAEFS
shows IVT values of 300-400 kg/m/s that are above the 90th
climatological percentile over much of Washington State. Heavy 
snow will spill over into the Northern Rockies Monday afternoon and
persist into Tuesday as a storm system in the Canadian Prairies 
keeps moist and upsloping NWlry 700-300mb flow over the Northern 
Rockies. Over the course of the next 72 hours, WPC PWPF above 
5,000ft in the Washington Cascades sports high chances (>70%) for 
snowfall totals >18". Similar high chance probabilities for >12" 
of snowfall over the next 72 hours are present over the Northern 
Rockies, especially in the Lewis Range, the Bitterroots, and Blue
Mountains at elevations >6,000ft. Treacherous travel conditions
around some passes in the northern Rockies and the Cascade Range
are possible. Farther south for elevations >7,000ft the Tetons, 
Wind River Range, and ridge lines in the northern Great Basin sport
moderate- to-high chances (50-70%) for >8" of snowfall through 
Tuesday afternoon.


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

Mullinax



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