Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
215 PM EST Tue Dec 24 2024

Valid 00Z Wed Dec 25 2024 - 00Z Sat Dec 28 2024


...The West...
Days 1-3...

An active pattern will continue for much of the West/Rockies over
the next few days as successive Atmospheric River events bring
mountain snow to much of the West outside the Southwest/SoCal. Lead
event today will continue to push farther inland and weaken with
light snow for the Idaho ranges into the Great Basin southeastward
into the Uintas/Wasatch and CO Rockies this evening/overnight.

By tomorrow late morning/early afternoon, the next wave of
precipitation will start to move into the WA/OR coast which will
start a relatively steady period of valley rain and mountain snow.
Snow levels tomorrow afternoon will start on the lower side
~2500-3500ft over the Cascades as light to moderate snow
overspreads the passes and mountains. However, snow levels will
rise through the night as milder air moves in, reaching
3500-5000ft, coinciding with the core of the AR (IVT values near
the 99th percentile). By Thursday, height falls will move ashore
with the upper jet curling across NorCal into the Great Basin,
promoting broad lift for areas of the interior West. Modest snow is
expected over the higher elevations from the Blue Mountains
eastward across Idaho and into western MT in addition to the
Trinity/Shasta/Siskiyous eastward to the Ruby Mountains and
northern Wasatch into the Tetons as the axis of moisture progresses
eastward.

Finally, by late Thursday into Friday, another Pacific system will
move into Vancouver with a robust surface low to the northwest of
WA and a modest plume of moisture into the Cascades/Olympics
southward to the NorCal ranges. Snow levels will vary but will
generally be a bit higher than the D1 system (3500-5500ft). Still,
snow will affect the higher passes in the West with some impacts to
travel.

WPC probabilities for at least 12 inches of snow through the 3-day
period are high (>70%) above about 3000-4000ft from north to
south. Total snow accumulation may exceed 3 to 5 ft in the higher
terrain of the Cascades. WPC probabilities for at least 6 inches
through the period are high (>70%) above about 3000-4000ft.

Fracasso