Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
238 PM EST Sun Nov 3 2024

Valid 00Z Mon Nov 04 2024 - 00Z Thu Nov 07 2024

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

An anomalous upper level low (NAEFS shows 500mb heights near the
1st climatological percentile over southwest New Mexico tonight)
will be the primary cause for periods of heavy snow in the higher
elevations of the Colorado and northern New Mexico Rockies. Periods
of snow ill pick up in intensity Monday morning along the Sangre De
Cristo, including around Raton Pass where treacherous travel
conditions are possible at pass level. Snow will taper off in these
areas by Monday afternoon. WPC PWPF shows moderate-to-high chances
(50-70%) for snowfall >8" along Raton Pass and at elevations
>9,000ft in the Colorado Rockies. In fact, there are moderate
probabilities (40-60%) for >12" above 10,000ft in central Colorado
and just west of Raton Pass. The Probabilistic WSSI shows moderate
chances (40-60%) for Moderate Impacts (hazardous disruptions to
daily life) in the Wet Mountains of Colorado and along Raton Pass.

Farther north, a potent shortwave trough over the northeastern
Pacific will race through Washington State on Monday with a plume
of Pacific moisture and modest surge in cold air advection
resulting in snow levels dropping as low as ~4,000ft. Heavy snow
Monday morning in the Cascades will linger into the afternoon hours
while the same moisture plume reaches the Northern Rockies Monday
afternoon, prompting periods of heavy mountain snow in the
Bitterroots, Lewis Range (including Glacier NP) and as far south as
the Sawtooth and Tetons. As low pressure strengthens over the
Canadian Prairies Monday night and into Tuesday morning, NWrly
flow will support multiple hours of upslope flow into portions of
the Northern Rockies.

By Tuesday afternoon, the upper low will begin to plunge south as
an anti-cyclonic wave break (ridging over the northeast Pacific
races over southwest Canada and forces the upper low south) leads
to a southward track in the cold front and another area of low
pressure forming in southeast Colorado by Tuesday night. This setup
will lead to periods of snow once again in the Central Rockies,
including the Palmer Divide and along both the Front Range of
Colorado and the Sangre De Cristo on Wednesday. WPC PWPF shows
high chances (>70%) for >8" of snowfall above 9,000ft. Along the
Palmer Divide and including the Denver/Boulder metro area, there
are moderate chance (40-60%) for snowfall total >4". The Palmer
Divide, given the higher elevation compared to Denver's metro area,
sport low chances (10-30%) for >8" of snow through Wednesday
evening.


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

Mullinax