Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 PM EDT Fri Nov 1 2024

Valid 00Z Sat Nov 02 2024 - 00Z Tue Nov 05 2024

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

A series of upper level disturbances will carve out a longwave
trough across the western third of the U.S. that will result in
periods of moderate-to-heavy mountain snow this weekend from the
Pacific Northwest to the Central Rockies. This afternoon and
through Saturday, mountain ranges such as the Cascades, northern
Sierra Nevada, Blue, Sawtooth, Bitterroots, Tetons, Wind River,
Lewis Range, and as far south as the Wasatch are all likely to see
measurable snowfall. Given the more supportive orthogonal flow
pattern into the Oregon Cascades, the Blue Mountains, and the
Boise/Sawtooth of Idaho, these mountain ranges have the higher odds
(high chances, or >70%) for snowfall >8" through Saturday
night. While the initial leading disturbance amplifies the
longwave trough over the Southwest U.S. Saturday evening, the next
trailing shortwave trough will arrive in the Pacific Northwest
bringing additional mountain snow to the Cascades and northern
Rockies through Sunday morning.

As the trailing disturbance dives southeast, it will further
deepen the longwave trough and foster an impressive area of upper
level divergence over the south-central High Plains. A surface low
in lee of the Rockies will strengthen over eastern Colorado while
500mb heights continue to fall across the Four Corners region
Sunday evening. By Sunday evening, 500mb and 700mb heights along
the Mexico/Arizona border dip to the 1st climatological percentile
according to the ECMWF SATs. As mid level moisture begins to wrap
around the 500mb low over central AZ and central NM Sunday night,
this should result in periods of heavy snow in parts of the
Southern Rockies. A little farther north, as high pressure builds
in over the northern High Plains, easterly upslope flow will
influence heavier snowfall along the Front Range of the Colorado
Rockies as well Sunday night and into Monday morning. By Monday
afternoon, the upper low exits to the east, and snowfall will
gradually taper off in the Central and Southern Rockies.

WPC PWPF from late Sunday and into Monday sports moderate-to-high
chances (50-70%) for snowfall >6" for elevations above 9,000ft in
the Colorado Rockies. This is also the case along the Sangre de
Cristo Mountains of northern New Mexico. Most of these mountains
ranges are showing moderate-to-high chances (50-70%) for Minor
Impacts according to the WSSI-P late Sunday into Monday. Residents
along the Palmer Divide of central Colorado and south towards Raton
Pass should also keep a close eye on this system for Sunday night
into Monday. This would be the first measurable snowfall of the
season for parts of these areas, and with low-to-moderate
probabilities (30-50%) present for snowfall totals >4", even
lesser snowfall totals could result in travel headaches for
commuters in these areas Monday morning.


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

Mullinax