Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EST Thu Dec 28 2023

Valid 00Z Fri Dec 29 2023 - 00Z Mon Jan 01 2024


...Northern New England...
Days 1-2...

Surface low pressure lifting northwest across the 40N/70W
Benchmark off the New England Coast will send precip over eastern
and upper Maine tonight with high pressure centered over the mouth
of the St. Lawrence River providing cold/dry air at the surface.
Freezing rain starts over these areas tonight as the milder
east-to-southerly flow atop a sufficiently cold boundary layer.
Day 1 WPC PWPF has further increased the potential for ice
accumulations >0.1" to a low-to-moderate risk of 40-80% centered
on north-central Maine.

Later tonight, a northern stream shortwave trough reaches central
Quebec and begins to dislodge the sprawling upper low from the
Midwest. Surface low development early Friday near the Adirondacks
 helps force precip in the cold sector, allowing light to locally
moderate snow in northern New England midday Friday through
Saturday. Day 2 snow probs for >2" are 40-60% over the White Mtns
of NH north through northern Maine. While this is not much added
snow depth, this would fall over most of the areas getting
freezing rain starting tonight which should make for enhanced
hazards to travel.


...California...
Days 2-3...

A full-latitude upper level trough approaching the West Coast
Friday will direct an atmospheric river north along West Coast
through Friday night with snow levels of 7000-8000ft generally
above coastal ranges. As the upper trough axis moves ashore early
Saturday, snow levels will gradually drop to 6000ft and SLRs will
incrementally increase as the atmospheric column cools and upslope
flow strengthens. By Saturday morning snow levels will fall to
around 6,000ft with precip beginning as snow along the higher
Sierra Nevada. Day 2 snow probs for >6" are 50-80% along the
length of the Sierra Nevada.


...Central Appalachians...
Day 2...

The upper low still producing snow bands over much of the Midwest
will continue to meander east across KY through Friday when it
begins to eject northeast on account of a northern stream
shortwave trough digging over Quebec and an increasing jet off the
Eastern Seaboard. Westerly flow on the back side of the trough
axis will allow upslope flow to bring snow to the central Apps
starting Friday evening. A quicker exit and less precip ahead of
the wave from 12Z guidance today has lowered the threat for >4"
which is now limited to around 20% in the southern Allegheny
Highlands near Snowshoe, WV on Day 2.


Jackson