Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Wed Nov 15 2023

Valid 12Z Wed Nov 15 2023 - 12Z Sat Nov 18 2023


...Northern Rockies...
Day 1...
Although focused a little farther north than previous runs, the
consensus of the overnight models still show a good signal for
moderate to heavy mountain snows impacting portions of northern
Idaho and northwestern Montana beginning later today and
continuing into early Thursday.  A mid-to-upper level shortwave
trough currently positioned over Southeast Alaska is forecast to
dig southeast across British Columbia before sweeping across the
northern U.S. Rockies late today into early Thursday.  Snow levels
are forecast to climb above 5000 ft before the associated front
pushes through the region this evening.  Heaviest accumulations
are expected to fall in and near the Glacier National Park region,
where favorable mid-to-upper level dynamics and a deepening
surface wave may help to bolster totals.  WPC probabilities
continue to show high probabilities (greater than 70 percent) for
accumulations of 4 inches or more covering much of the region. 
This includes Marias Pass.  Locally heavier accumulations can be
expected, especially in the higher terrain north of the pass,
where WPC probabilities show a high risk for accumulations of 8
inches or more.

...Sierra Nevada...
Day 1 and 3...
A shortwave ejecting out ahead of a slow-moving low centered over
the eastern Pacific is expected to bring light to moderate
precipitation into the Sierra later today, with heavier totals in
the central and southern Sierra.  With snow levels expected to
remain above 8000 ft for much of the central and southern Sierra
and above 7000 ft in the northern Sierra, widespread impacts are
not expected.

Following a day of more tranquil weather, precipitation is
forecast to return to the area as the parent low moves toward the
coast late Friday and early Saturday.  However, models disagree on
the timing of this system, so there is a fair amount of
uncertainty regarding how much precipitation will spread into
region late in the period.

Pereira