Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Sat May 06 2023

Valid 12Z Sat May 06 2023 - 12Z Tue May 09 2023

...Western U.S....
Days 1-3...

Strong upper ridging/upper high over central Canada will favor
continued troughing over the Western CONUS this weekend into
Monday, maintaining an unsettled period for the mountainous West
and the northern and central Rockies. Moisture will be limited
with the source region from the Gulf of Alaska, but combination of
broad upper divergence and upslope enhancement will promote
generally light to modest snowfall. D1 will feature a continuing
elongated vort max into NorCal with an upslope focus on the
northern Sierra, where more than 6 inches of snow is likely for
the higher elevations. Snow levels will dip to around 5000ft early
this morning, with a slight rebound during the day. D1
probabilities of at least 4 inches of snow are high (>70%) in the
northern Sierra above about 7000ft and also across central NV.
Farther north into the northern Great Basin and northern Rockies
through Day 2, the lead-in vorticity will weaken and lift
northeastward, with generally low-to-medium probabilities (<40%)
for 4 inches of snow across the northwestern Montana and central
Idaho ranges, as well as the greater Yellowstone region of
south-central MT and northwest WY. Into D3, a weakening upper low
will move into NorCal, spreading additional snowfall across
elevations generally above 4500ft in the Shasta-Siskyous, northern
Sierra, and OR Cascades as the vort max moves eastward at a
progressive clip.

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

Fracasso/Snell