Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Mon Feb 06 2023

Valid 12Z Mon Feb 06 2023 - 12Z Thu Feb 09 2023


...Pacific Northwest to the Northern Rockies...
Days 1-3...
An elongating, positively-tilted upper trough will continue to
move across the West, supporting some additional, mainly light
snow across the Rockies today.  In its wake, an upper ridge will
move onshore, with dry conditions expected along much of the West
Coast.  Western Washington and Oregon will remain an exception,
with warm advection and onshore flow ahead of the next system
supporting the persistence of unsettled weather.  Precipitation is
expected to be relatively light during the day before increasing
in intensity Monday night and continuing through Tuesday as an
amplifying shortwave trough and its associated frontal band impact
the region.  Periods of heavier precipitation are expected as the
system moves across the region.  Snow levels, which are expected
to be around 3500-4000 ft at the start of the event are forecast
to drop closer to 1500-2000 ft as the front pushes across the
region.  The heaviest snowfall accumulations are expected to occur
across the Olympics and the northern Cascades, where snowfall
rates may exceed 2 in/hr on Tuesday, supporting accumulations of
several feet across the higher terrain.  As snow levels fall, the
northern Cascades passes are likely to be impacted as well, with
several inches possible.  Relatively lighter, but impactful
amounts are expected farther east across portions of the northern
Rockies as well, particularly the northern Idaho and northwestern
Montana ranges, where several inches of snow are likely.  Snows
are forecast to diminish from west to east as the upper trough
continues to move east on Wednesday, replaced by an amplifying
upper trough moving across the region on Thursday.

The probability of significant icing is less than 10 percent.

Pereira