Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
219 AM EST Sat Dec 16 2023

Valid 12Z Sat Dec 16 2023 - 12Z Tue Dec 19 2023

...Great Lakes to the Central and Southern Appalachians...
Days 2-3...
A powerful low that is expected to bring heavy rain to much of the
East Coast is forecast to track from the Southeast late in the
weekend to the St Lawrence Valley by Monday evening.  Behind this
system will be an amplifying shortwave that is forecast to plunge
southeast from central Canada through the upper Great Lakes and
into the Ohio Valley on Monday, with a deep closed low developing
over the Mid Atlantic and the Northeast by early Tuesday.  Strong
ascent and intense cold air advection associated with this system
will produce lake effect snows, developing initially over the
favored northwest snow belts of Lake Superior Sunday night before
spreading further downstream off of lakes Michigan and Erie on
Monday.  There the deep northwest fetch will support an upstream
connection to the northern lakes, helping to maintain ample low
level moisture.  The sharp contrast between some of the coldest
air of the season and the still warm lake temps will support an
unstable environment capable of producing heavy rates.  Some of
the heaviest totals of this event are likely to occur along the
favored upslope regions of the central Appalachians.  WPC PWPF
shows high probabilities (greater than 70 percent) for snowfall
amounts of 4 inches or more along the Allegheny Mountains from far
western Maryland to southeastern West Virginia.  Embedded within
this area are high probabilities for accumulations of 8 inches or
more centered over West Virginia.  In addition to areas of heavy
snow, a tight pressure gradient between the departing low and high
pressure centered over the Plains will support strong, gusty winds
throughout the region.

...Sierra...
Day 3...
A weakening closed low lifting northeast ahead of a second closed
low dropping southeast through the northeastern Pacific will bring
areas of heavy precipitation to Northern California on Monday,
continuing in Tuesday.  However, snow levels above 7000ft and
rising to above 8000ft in many locations will limit any widespread
heavy snow impacts.

Pereira