Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
404 PM EDT Fri May 05 2023

Valid 00Z Sat May 06 2023 - 00Z 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 mountains of the
West into 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 an
elongated vort max into NorCal with a focus on the northern Sierra
where more than 6 inches of snow is likely for the higher
elevations. Snow levels will dip to below 5000ft as the colder
thicknesses move in overnight into early Saturday, with a 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. For D2, the lead-in vorticity will weaken and
lift northeastward, with generally low probabilities for 4 inches
of snow across the northern Great Basin. Into D3, a weakening
upper low will move into NorCal, spreading additional snowfall
across 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