Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
338 PM EST Mon Dec 18 2023

Valid 00Z Tue Dec 19 2023 - 00Z Fri Dec 22 2023

...Eastern Great Lakes, Ohio Valley, and the Central to Southern
Appalachians...
Day 1...

Closed upper low over north-central OH this afternoon shifts east
over the Mid-Atlantic through Tuesday as the surface low
(currently over southern New England) shoots north to the mouth of
the St. Lawrence by this evening. CAA across the Northeast brings
in steepening lapse rates through tonight and the upper level
low/PVA provides lift through the DGZ supporting lake enhanced
snow showers with locally intense rates. The westerly flow south
of upper low becomes NWly by this evening with ample upslope flow
to the central/southern crest of the Appalachians and LES for NWly
flow snow belts off Lakes Erie and Ontario.

Day 1 snow probs for >6" after 00Z is moderately high (50-80%)
east of Lake Erie with low to moderate (30-50%) for the Buffalo,
NY metro and central WV highlands. Ridging spreads in Tuesday
providing a fairly quick shutoff to LES and upslope snow.


...Sierra Nevada...
Days 1-3...

A shortwave trough pushes into the OR/CA coastal border this
evening with a stronger, deeper low pushing south well off the
PacNW coast, shifting off the northern CA coast Tuesday, then
slowly off the southern CA coast through Thursday. Ample Pacific
moisture spreading inland ahead of these systems maintains snow
levels between 7000-8000ft through the forecast period along the
Sierra Nevada crest. Days 1-3 snow probs for >6" are moderate to
high (50-80%) inching south from the central to southern Sierra
Nevada with 3-day totals of 1-2ft for the higher elevations.


...Pacific Northwest...
Day 1...

Expect generally light precipitation to spread north as a
shortwave associated with the remnants of the previously noted
upper low lift across the region.  High snow levels will further
preclude heavy snow impacts, however guidance continues to raise
some concerns for light icing along the eastern slopes of the
southern Washington and northern Oregon Cascades into the Columbia
Gorge. Trapped cold air is expected to produce areas of freezing
rain, with Day 1 WPC PWPF showing lower (20-40%) probabilities for
ice accumulations of >0.10".


Jackson