Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 PM EST Wed Dec 04 2019

Valid 00Z Thu Dec 05 2019 - 00Z Sun Dec 08 2019

Days 1-3...

...Great Lakes to the Central Appalachians...

Northwest flow will continue to support snow showers into
Thursday.  A reinforcing shot of colder air associated with a mid
level shortwave dropping southeast across the Great Lakes will
help support better organized lake effect snows southeast of the
lower Great Lakes Wednesday night.  Orographic lift will continue
to support locally heavy amounts along the Allegheny Mountains
from southwestern Pennsylvania to eastern West Virginia.  Snows
are expected to diminish as a shortwave ridge moves east across
the region on Thursday.  However, snows are expected to quickly
return to the region as clipper system drops through on Friday.  

...Southwest to the Central Rockies...
An mid to upper level low will continue to weaken as it moves
progressively east from California through the Great Basin
overnight.  This is expected to produce locally heavy high
elevation snows from eastern Nevada to the western Colorado and
far northern New Mexico Rockies.

...Northern California to the Sierra...
A deep upper low is expected to gradually drift toward the
Northern California and Oregon coasts on Friday.  Deep
southwesterly flow ahead of the low will begin to support moderate
to heavy precipitation across portions of Northern California by
late Friday.  With snow levels around 6000ft, heavy snows through
late Friday will be mainly confined to the higher elevations of
the Siskiyou/Shasta-Cascade region.  Although models show the
system weakening as it moves onshore on Saturday, moderate to
heavy precipitation is expected to extend south along the Sierra,
with heavy snow accumulations likely - especially for areas above
6000ft.

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

Pereira