Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
234 AM EST Sun Dec 31 2023

Valid 12Z Sun Dec 31 2023 - 12Z Wed Jan 03 2024

...Great Lakes & Central Appalachians...
Days 1-2...

A clipper system tracking through the Great Lakes this morning is
channeling a brisk northeasterly wind over Lakes Superior and
Michigan. This clipper will spark numerous snow showers across the
Great Lakes, but it is on the western flank of the clipper where
winds racing over Lake Michigan could produce minor snowfall
accumulations today and this evening. Latest WPC PWPF shows
low-to-moderate chances (30-50%) for snowfall totals >2" along the
Wisconsin coast and as far south as northwest Indiana. Meanwhile,
the central Appalachians are next in line for periods of snow as
the clipper tracks across the northern Mid-Atlantic Sunday night
and into Monday morning. Cold air advection at 850mb and WNW
upsloping winds will support periods of moderate-to-heavy snow
from the Potomac Highlands on north to the Laurel Highlands in
southwest Pennsylvania Monday morning. WPC PWPF shows low chances
(10-20%) for >4" totals in some of the higher peaks and more
topographically-favored upslope areas of eastern West Virginia,
Garrett County, Maryland, and the Laurel Highlands. Confidence is
a higher in totals topping 2" as WPC PWPF shows moderate-to-high
chances (50-70%) for snowfall totals >2". The WSSI does depict
Minor Impacts in these areas through Monday evening, suggesting a
few inconveniences to daily life (most notably the potential for
hazardous travel conditions) are anticipated.

...California...
Day 3...

Another Pacific upper low barreling into the West Coast will
direct a plume of 850-700mb moisture flux into California via
brisk SSW flow. Details on the arrival of precipitation are not
fully resolved yet as some guidance is faster with the
precipitation's arrival (ECMWF), while  the GFS/CMC camps keep
precipitation from reaching the Golden State until Wednesday
morning. Still, there are enough members in the WPC super ensemble
that show the precipitation arriving early enough to cause WPC
PWPF to depict low risks (10-30%) for >4" of snowfall in the
Shasta/Trinity/Salmon mountains of northern California Tuesday
night. Snowfall reaching the Sierra Nevada is likely to hold off
until later in the day on Wednesday as the upper low inches closer
to shore. While the start of the snowfall remains in question,
most guidance is in better agreement that Wednesday looks to be
the snowiest day as the upper level low finally moves over overhead

The probability of significant ice across the CONUS is less than
10%.


Mullinax