Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
428 AM EST Mon Dec 03 2018

Valid 12Z Mon Dec 03 2018 - 12Z Thu Dec 06 2018

...CA Ranges Days 1-3...

Monday night through Wed, a closed mid-level low and associated
surface reflection will drop southward  offshore the coast of
California. Moisture will stream onshore ahead of this circulation
and inland into the Sierra Nevada range of California.  Periods of
700 mb convergence and theta-e advection help drive ascent, with
periods of snow at higher elevations both Tue and Wed. WPC
probabilities for 4 inches of snow are moderate for portions of
the central and southern Sierra Nevada range both Tue and Wed.

...Ranges of northern UT/northern CO/southern WY Day 3 ...

Also during day 3, mid-level moisture will stream eastward across
UT into the Medicine Bow mountains/Snowy Range near the southern
WY/northern CO border. Light snow are forecasts with favored
upslope areas targeted for enhanced probabilities for 4 inches on
Wed.

...Great Lakes ...

A cold front crosses the northeast today. Trajectories behind the
front will become aligned along the Lakes to produce light lake
effect snow off lakes Erie and Ontario into the Tug Hill Plateau,
where higher probabilities for 4 inches of snow exist on day 1.
Modest light snow showers extend into the central Appalachians as
well. Snow on days 2-3 are expected to be light, with light snow
picking up in the Keweenaw peninsula of the western UP of MI as a
cold front passes, with light snows occurring both with the front
and also with lake enhancement following the front. Probabilities
less than 10 percent for 4 inches of snow.

The probability of significant icing (0.25 inches or more) is less
than 10 percent days 1-3.

Petersen