Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 AM EST Sat Feb 24 2024

Valid 12Z Sat Feb 24 2024 - 12Z Tue Feb 27 2024


...Pacific Northwest and California to the Central Rockies... 
Days 1-3... 
Unsettled weather, including high-elevation heavy snow, is
expected to return to portions of the northern Cascades and the
far northern Rockies today, before spreading south as an amplified
shortwave trough digs south from the Gulf of Alaska through
British Columbia on Sunday. 

On Sunday, heavy snow is likely to cover the Olympics, while
spreading south through the Washington into the Oregon Cascades
and along the northern Idaho, and northwestern Montana Rockies. 
By early Monday, snow accumulations of a foot or more are likely
for Snoqualmie and Stevens passes, while multiple feet can be
expected in the higher elevations of the northern Cascades.  Light
accumulations are possible in the lowlands as snow levels drop
below 500 ft in western Washington behind a sharp cold front.  In
the northern Idaho and Montana ranges, widespread accumulations of
6 inches or more are likely, including at both Lookout and Marias
passes, with a foot or more expected in some of the neighboring
higher elevations. 

Snow will continue to spread further south and east on Monday, as
the upper trough continues to dig across the western U.S.  As
heavy snow continues for portions of Cascades and northern
Rockies, periods of heavy snow will accompany a strong cold front
as it plunges south into northern California, the Great Basin, and
the central Rockies.  Areas impacted will likely include the
Sierra, the northeastern Nevada mountains, and the Rockies as far
south as the San Juans.  WPC PWPF shows at least moderate
probabilities (40 percent or higher) for accumulations of 8 inches
or more across portions of these areas.  While the heavy snow
accumulations will be confined to the mountains, many valley
locations may see some light accumulations as snow levels plunge
into the valley floors behind the front.  Meanwhile portions of
the Oregon Cascades will likely see additional heavy amounts,
especially the Oregon Cascades, where accumulations of 8 inches or
more are likely to impact the passes on Monday.

Models continue to indicate that low-level potential instability,
moisture, and winds will support periods of brief, but intense
snowfall with gusty winds.  Snow Squall Parameter guidance from
the GFS and NAM continue to indicate that conditions will be
favorable for snow squall development over portions of the
northern Rockies, Oregon Cascades, and the northern Intermountain
West by early Monday before shifting further south along with the
front into the central Great Basin and Rockies later in the day
into Monday night.
 
The probability of ice accumulations of 0.10 inch or more is less
than 10 percent. 
 
Pereira