Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 AM EDT Mon May 08 2023

Valid 12Z Mon May 08 2023 - 12Z Thu May 11 2023

...Northern California to the Northern Rockies....
Days 1-2...

A compact, deep upper-low moving inland near the Oregon-California
border this morning is forecast to lift northeastward into the
northern Great Basin by Tuesday while weakening within a broader
upper-level trough off the West Coast. This system will spread
chances for moderate to locally heavy snow across elevations
higher than 4000-5000ft from northern CA through OR and central
ID. This includes the Klamath Mountains, Shasta Cascade, and the
southern Oregon Cascade regions, where WPC probabilities for at
least 4 inches of snow are medium (>40%). Elsewhere, mostly light
amounts are forecast across the higher elevations of the region,
with widespread heavy amounts not expected.

...Northern and Central Rockies...
Day 3...

The next shortwave to round the base of the West Coast trough is
anticipated to take a more amplified trek and dive across the
Southwest on Wednesday until taking on a negative tilt over the
southern/central Rockies Wednesday night. Moisture availability
will be plenty with return flow from the Gulf of Mexico solidly in
place, a coupled jet streak over the central Rockies promoting
ample upper diffluence, and upslope flow to the north of a
developing surface low over the central High Plains. However,
unsurprisingly given the time of year, snow levels will be very
high across the Rockies and start around 10000ft before slightly
falling to around 9000ft by the end of D3. The greatest chances
for more than 4 inches of snowfall (10-30%) through Thursday
morning will reside across the Absaroka and Wind River Ranges, as
well as the Bighorns of WY. Heavy snow chances are likely to
continue into D4 throughout the highest elevations (>9000ft) of CO
and WY.

The probability of ice accumulations greater than 0.25 inch is
less than 10 percent.

Snell