Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
258 PM EST Fri Dec 29 2023

Valid 00Z Sat Dec 30 2023 - 00Z Tue Jan 02 2024

...California...
Day 1...

A full-latitude trough approaching the West Coast this afternoon
will reach the northern/central California Coast tonight. An
atmospheric river with 1" PW continues to be drawn up the West
Coast ahead of the trough axis with the focus tonight into CA. As
the upper trough axis approaches the Sierra Nevada tonight, snow
levels will drop from about 7500ft to around 6000ft as the
atmospheric column cools and upslope flow strengthens. Heavy snow
falls above the snow levels on the Shasta/Siskiyou tonight and the
length of the Sierra Nevada Saturday morning with Day 1 WPC snow
probs for >6" generally 40 to 70% over these ranges. Treacherous
travel and delays over the higher Sierra Nevada are anticipated
late tonight into Saturday afternoon.


...Northern New England...
Day 1...

Moderate snow at times tonight over northern Maine to the White
and Green Mtns as a northern stream trough approaches from Quebec.
Related surface low pressure develops over the Gulf of Maine
tonight and quickly shifts northeast. Snow will wind down by
Saturday evening as the strongest forcing quickly moves east over
the Atlantic Canadian Maritimes. Day 1 WPC PWPF for >4" 10-20%
over far northeast Maine - north of Caribou. However, this snow
will be on top of the ice that glazed some of this area today,
increasing travel impacts.


...Central Appalachians...
Days 1 and 3...

An upper low over KY opens into a trough as it shifts east over
the Mid-Atlantic tonight with upslope flow for central WV into
western MD bringing snow this evening through midday Saturday. Day
1 WPC PWPF for >4" have smoothing issues over this narrow strip of
highlands, with 40-60% showing up in a small area around Snowshoe,
WV.

A Clipper coming out of Saskatchewan today will cross the Great
Lakes Sat/Sun before crossing the central Appalachians Sunday
night and bringing a brief bout of upslope snow. There are some
single digit Day 3 PWPF values for >4" from the Lauren Highlands
of PA through the Allegheny Highlands of WV.



Jackson