Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 PM EST Tue Dec 03 2019

Valid 00Z Wed Dec 04 2019 - 00Z Sat Dec 07 2019

Days 1-3...

...Great Lakes/Central Appalachians...
A shortwave trough currently centered over the western Great Lakes
is expected to move east through the evening hours on Tuesday. 
Weak synoptic lift along with modest lake enhancement is expected
to support light snows in the lee of the lower Great Lakes
overnight.  Meanwhile, upstream energy currently centered over
southern Canada will continue to drop southeast into the upper
Great Lakes Wednesday night.  Deepening moisture and modest cold
air advection aloft will support snow showers with generally light
accumulations in the northwest snow belts of northern Michigan. 
As this energy continues to dig southeast and cold air deepens on
Wednesday, expect lake enhanced showers to become better organized
east of the lower Great Lakes, with orographic lift helping to
bolster accumulations along the Allegheny and Tug Hill plateaus -
where several inches are possible before snow begins to wane on
Thursday.  Northwest flow will also support accumulating snows
along the Allegheny Mountains, with several inches possible across
the Laurel Highlands south into West Virginia.  Wintry weather is
expected to quickly return on Friday however as a fast moving
upstream shortwave amplifies over the Great Lakes, supporting
additional light accumulations east of the lower Great Lakes.

...Southern California to the Central Rockies...
An upper low settling south over the eastern Pacific is expected
to weaken and move east across California on Wednesday.  High
elevation snow, with several inches possible, is expected over the
southern Sierra, as well as the San Gabriel, San Bernadino and San
Jacinto mountains in Southern California.  As the system continues
east, locally heavy accumulations are possible across the higher
elevations of the southern Nevada mountains to the western
Colorado ranges on Thursday.

...Northern California...
Strong southwest flow ahead of an approaching low will bring
moderate to heavy precipitation into Northern California on
Friday.  High elevation heavy snow is possible along the
Siskiyous-Shasta Cascade region.

For Days 1-3, the probability of significant icing (0.25-inch) is
less than 10 percent.

Pereira