Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Mon May 08 2023
Valid 00Z Tue May 09 2023 - 00Z Fri May 12 2023
...Oregon and Idaho....
A compact upper-low over the Oregon-California border this
afternoon will shift east-northeast to central Idaho through
Tuesday morning while weakening within a broader upper-level
trough off the West Coast. This system will spread moderate to
locally heavy snow to elevations above 4500ft across the Greater
Blue Mountain region of OR and the Sawtooth and Salmon River
Mountains of Idaho where Day 1 WPC probabilities for >4" snow are
moderate (30% to 60%). Lighter snow will spread to terrain the
Idaho/Montana border and into Northwest Wyoming.
...North-Central and Colorado Rockies...
A reinforcing shortwave trough currently well off the OR/CA coast
continues to amplify as it shifts southeast, crossing SoCal
Tuesday night, forming the base of the West Coast trough as it
then shifts east to NM through Wednesday night where it takes on a
negative tilt. Moisture availability for the Rockies 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
lee-side low over the central High Plains. Unsurprisingly given
the time of year, snow levels will be around 10000ft ahead of
precip late Wednesday, falling to about 8500ft Wednesday night.
Day 3 probabilities for >4" are moderate over much of the CO
Rockies as well as the highest Wind River, Absaroka, and Bighorn
Ranges, as well as the Bighorns of WY. Locally heavy snow threats
continue through Thursday night for the Front Range and Laramie
The probability of ice accumulations greater than 0.25 inch is
less than 10 percent.