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Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 PM EST Sun Mar 03 2024

Valid 00Z Mon Mar 04 2024 - 00Z Thu Mar 07 2024

...West Coast & Northern/Central Rockies...
Days 1-3...

The longwave trough over the Pacific Northwest will maintain a
persistent influx of 700mb moisture to the north of a stationary
front draped west-to-east from the Sierra Nevada to the CO Rockies
through today. Combined with added lift via
topographically-favored upslope flow, this will keep periods of
moderate-to-heavy snow ongoing this afternoon and into this
evening from the Sierra Nevada, the northern CA Coastal Range, and
Wasatch to the Tetons and CO Rockies. Latest WPC PWPF through
Monday afternoon continues to show high chances (>70%) for
additional snowfall amount >8 inches along the northern Sierra
Nevada above 5,000ft. With most snowfall expected to occur this
afternoon and evening, the Wasatch >7,000ft feature moderate
chances (40-60%) and CO Rockies >9,000ft moderate-to-high chances
(50-80%) for additional snowfall totals >6 inches. Snowfall rates
will diminish late Sunday night and Monday morning from the Sierra
Nevada to the CO Rockies.

By late Monday morning, however, any break will short lived in
northern CA, southern OR, and into the interior Northwest as
another 500mb shortwave on the backside of the longwave upper
trough positioned over the the northwestern U.S. and southwestern
Canada pivots towards the Pacific Northwest. While not nearly as
vigorous as the shortwave trough late Friday into Saturday 
morning, added 500mb PVA and another surge in 850-700mb moisture
is set to track through these aforementioned regions late Monday
morning and into Monday afternoon. As a weak frontal boundary
forms Monday night and becomes positioned from the OR/CA border on
east to the Tetons, it will act to give additional lift at low
levels to foster heavy snow from the northern CA mountains
(Salmon, Shasta), the northern Sierra Nevada, and on north along
the Cascade Range to as far inland as the Boise/Sawtooth mountains
and the Tetons. WPC 48-hr PWPF (00Z Mon - 00Z Wed) depicts high
chances (>70%) for >18 inches along the northern Sierra Nevada and
neighboring northern CA ranges on north along the Oregon Cascades.
With the event picking back up in the Boise/Sawtooth mountains
Monday night into Tuesday, WPC 24-hr PWPF shows low-to-moderate
chances (30-50%) for additional snowfall totals >12 inches there.

From Tuesday night into Wednesday, as an upper low approaches CA,
the stream of Pacific moisture into the Intermountain West will
show signs of concluding with less in the way of heavy snowfall
from CA to the central Rockies on Wednesday. Snow will be heaviest
from southern OR to central WY Tuesday night into early Wednesday
morning as residual 700mb moisture tracks west to east. As the
upper low tracks south along the CA coast, the 700mb moisture
transport will wrap around the low rather than be oriented east
into the Intermountain West. WPC PWPF shows the Tetons, Absaroka,
Bear River Range, and Wind River Ranges with moderate-to-high
chances (50-80%) for >8 inches between 00Z Wed - 00Z Thurs. The
Trinity/Shasta and northern Sierra Nevada in northern CA also show
moderate-to-high chances (50-80%) for >8 inches, although the bulk
of that snowfall is expected between 00-12Z Wed.

Mullinax