Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
352 AM EST Fri Dec 02 2022

Valid 12Z Fri Dec 02 2022 - 12Z Mon Dec 05 2022

...Pacific Northwest, California, Central and Northern Rockies...

Days 1-3...
Lead system responsible for the heavy Sierra snow early Friday
will shift its focus to the Great Basin and central Rockies today
as the upper trough and surface cold front progress eastward.
Modest snow amounts are expected in the central/southern Sierra
early Day 1, across parts of Utah, and over much of the Colorado
Rockies. Height falls and ample moisture will complement
lower-level frontogenesis and orographic upslope over these and
other higher elevations along and behind the cold front. WPC
probabilities for at least 8 inches of snow are highest over the
Elk Mountains in Colorado.

Also on Day 1, another upper low will sink slowly southward along
130W just offshore WA/OR today into early Saturday. With a track
this far offshore, QPF will be mostly confined to the Olympics as
a narrow moisture axis brings in significant accumulations. WPC
probabilities for at least 8 inches of snow are high across the
Olympics. By Day 2, the upper low will continue to wobble
southward of the coast as the tail-end of the lead Day 1 system
off California brings in another wave of precipitation into the
Golden State, focused primarily over the Sierra but also into the
Shasta Siskiyous and Klamath Mountains. By Day 3, the upper low is
forecast to weaken and the larger trough elongate eastward,
spreading moisture farther east across the Great Basin into the
Wasatch northward through western Wyoming, especially the Tetons.
WPC probabilities for at least 8 inches of snow are high (>70%)
over the Sierra Days 2 and 3, and moderate (>40%) to high for at
least 12 inches of snow. From northern UT northward, WPC
probabilities for at least 6 inches of snow are moderate.

...Northern Minnesota/Wisconsin and the U.P. of Michigan...

Day 1...
A quickly-moving positively-titled trough will race through the
Northern Plains/Upper Midwest/western Great Lakes later today into
Saturday. Modest upper divergence will promote some broad-scale
lift as the northern stream jet retreats and weakens. At the
surface, low pressure out of Montana and northeastern Wyoming will
lift northeastward across the Dakotas into Minnesota with an area
of accumulating snow to the northwest of the low. Ratios will rise
as colder air moves in but at the same time as QPF
exits/diminishes. WPC probabilities for 4 inches or more of snow
are low across much of northern MN, with slightly higher
probabilities over the western U.P. of Michigan due to additional
lake effect once cold air sweeps in behind the system on Saturday.
Gusty winds may accompany this system and increase potential
travel hazards within any localized areas experiencing modest
snowfall rates due to blowing snow.


For Days 1-3, the probability of significant icing exceeding 0.10
inch is less than 10%.


Fracasso