Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
301 AM EST Sun Nov 15 2026

Valid 12Z Sun Nov 15 2026 - 12Z Wed Nov 18 2026

...Western United States...
Days 1-3...

An active storm track, courtesy of a strong Pacific jet stream,
will direct yet another storm system at the West Coast today. An
atmospheric river (AR) associated with a potent northeast Pacific
cyclone will continue to impact the West Coast early this morning
with CAA in wake of the storm's cold frontal passage causing snow
levels to lower over the Cascades, Olympics, and Siskiyou/Shasta
mountains through Sunday night. The air-mass is not especially
cold, considering the source region is from the North Pacific, so
snow levels in the Cascades, Olympics, and southward to the
Siskiyou/Shasta/Salmon mountains of northern CA are generally
expected to hover around 4,000ft at the lowest through the start of
the week. Precipitation is also expected to wane across the
Cascades of OR/WA by early Monday. Probabilities for snowfall
totals >6" are >30% for elevations above 5,000ft.

The footprint of the AR will stretch southward into the Sierra
Nevada with the heaviest snowfall expected Sunday night and into
the day on Monday. Snow levels as low as 5,000ft are possible in
the northern Sierra Nevada, but areas of heavier snowfall are
likely to reside at/above 6,000ft in elevation. Latest
probabilities show moderate-to-high chances (50-80%) for snowfall
totals >6" along I-80 near Donner Pass and low-to-moderate chances
(20-40%) along US-50 near Phillips and Twin Bridges. WSSI-P shows
greater confidence in Minor Impacts (winter conditions; use caution
while driving) at these aforementioned CA passes (50-70% odds),
but it is noteworthy that there are low chances (10-30%) for
Moderate Impacts which suggest the potential for travel
disruptions.

The AR works its way farther inland across the Great Basin and
northward across the Blue Mountains and Northern Rockies beginning
Sunday night. The upper trough slows down as it moves into the
Intermountain West late Monday and into Tuesday, providing a
prolonged window for light-to-moderate snowfall rates across the
mountain ranges through the first half of the week. The mountains
ranges seeing the longest period of favorable upper-level
divergence, anomalous moisture aloft, and upslope enhancement are
the Blue and Sawtooth Mountains. Latest probabilities depict high
chances (>70%) for >8" of snow in the Blue Mountains and moderate
chances (40-60%) for snow totals >12" at/above 6,000ft. By Monday
night, PWs across the Northern Rockies approach the 97.5
climatological percentile, providing more than enough moisture to
support accumulating mountain snow. The AR will have cleared the
Sierra Nevada by Tuesday morning and mountain snow will work its
way east across the Great Basin and towards both the Wasatch and
Uinta, eventually clipping the central Rockies and San Juans of CO
early Wednesday as well for elevations mostly above 8,000 ft.
Latest probabilities show high chances (>70%) for >6" of snow in
the southern reaches of the Wasatch and the more remote elevations
of the Bitterroots. Some minor snowfall amounts (generally less
than 2") in the valleys of western MT at elevations as low as
3,000ft, but most heavy snowfall amounts will reside above 7,000ft
in the Bitterroots late Monday into Tuesday.

...Northern California...
Day 3...

Next system to impact the West Coast will begin to bring
precipitation inland across Northern California early Wednesday
before spreading heavy snow across the Sierra Nevada into the
medium range time frame (Day 4). Current ECENS probabilities for
the landfalling AR across northern CA just prior to 12Z Weds
depict 40-60% chances for IVT values >500 kg/m/s. This AR will be
associated with another upper-low diving southeast out of the Gulf
of Alaska and strengthening within the persistent troughing located
across the western United States. This will allow for snow levels
to start out around 4,000-4,500 ft and could lower down to around
3,500 ft within heavier snowfall rates in northern CA, allowing
for potential snowfall impacts at major mountain passes along I-5.
24-hr snowfall probabilities by 12Z Weds are already high (60-90%)
across the Shasta Siskiyou, with additional snowfall likely after
12Z Weds.


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


Snell/Mullinax