Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
226 PM EST Tue Nov 18 2025

Valid 00Z Wed Nov 19 2025 - 00Z Sat Nov 22 2025

...California through the Southern Rockies...
Days 1-3...

A series of upper lows tracking into the southwestern U.S. will
continue through the remainder of the work-week that will keep
mountain snow in the forecast from the Sierra Nevada and the peaks
of the Transverse Ranges to as far east as the CO/NM Rockies.

The current stretch of active weather is due to an upper low over
southern CA that is directing a swath of rich subtropical moisture
and generating large-scale vertical ascent over the Southwest. A
lack of a sub-freezing antecedent air-mass is making the more
remote mountains ranges of the southern Sierra Nevada, northern AZ,
southern UT, and CO's San Juan Mountains as the favored locations
for measurable snow through Wednesday evening. By Wednesday night,
the 500mb upper low opens up into a potent shortwave trough that
takes on a negative tilt over the Gulf of California, resulting in
increased divergence aloft and a healthier influx of moisture into
the southern Rockies. While snow levels may dip to as low as
7,000ft
in parts of NM and CO, the bulk of the heavier snowfall totals
will be confined to elevations above 9,000ft in the San Juans and
Sangre De Cristo. The heaviest snowfall transpires in these
mountain ranges on Thursday and persists with lighter amounts into
Friday morning. WPC probabilistic guidance shows moderate-to-high
chances (50-80%) for snowfall totals >8" and low-to-moderate
chances (20-40%) for snowfall totals >12" for elevations above
9,000ft in southern CO and northern NM, while similar probabilities
for snowfall totals >8" also exist for southern UT mountain ranges
above 8,000ft.

At the same time as the current upper-level trough goes negative
tilt over northern Mexico early Thursday morning, another upper low
off the West Coast tracks south along the CA coast on Thursday. By
Friday, the upper low is forecast to reside over the southern CA
coast with a near carbon-copy setup to Tuesday's upper-level
pattern. Snow will start to unfold in Salmon/Trinity/Siskiyou of
northern CA early Thursday morning, followed by the Sierra Nevada
throughout the daytime hours on Thursday. Snow levels may dip as
low as 5,000ft, but only minor snowfall accumulations are
anticipated below 6,000ft. The heavier snowfall totals are most
likely to unfold at elevations above 7,000ft in the Sierra Nevada
through Friday morning. This new upper-low will perform a similar
synoptic-scale evolution to Tuesday's low, but this time it will
track a little farther south and west, resulting in lesser
concerns for snow in the higher mountain ranges of southern NV,
northern AZ, and southern UT. WPC probabilities depict moderate
chances (40-60%) for snowfall totals >4" along the Sierra Nevada
above 7,000ft with low chances (10-30%) for elevations >9,000ft in
the southern Sierra Nevada receiving >8" of snow. The peaks of the
San Gabriel and San Bernadino Mountains (above 7,000ft) also have
moderate chances (40-60%) for snowfall totals >4" late Thursday
night and into Friday.


Mullinax