Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
215 PM EST Sat Dec 09 2023

Valid 00Z Sun Dec 10 2023 - 00Z Wed Dec 13 2023

...Michigan U.P...
Days 1 & 3...

Pair of mid-level vort maxes will dumbbell past each other this
evening, with the farther east system ultimately carrying sfc low
pressure into Canada. Wrap-around flow in combination of the
farther west vort max pushing through WI overnight will favor lake
effect snow across the northern U.P. of Michigan on N to NW flow.
Lake-850 delta Ts increase to about 10C overnight with sufficient
moisture until heights rise by late afternoon Sunday, helping to
end any appreciable snow. WPC probabilities for at least 4 inches
of snow are moderate (40-70%) over the Porcupine and Huron
mountains as well as east of Marquette.

On Day 3, an upper low will move from Manitoba into northwestern
Ontario with a surface cold front dropping through northern MN and
into the western Great Lakes. 850 temps will be colder with this
wave, dropping to around -12 to -15C and supporting WNW to ESE
bands post-FROPA Tuesday afternoon. WPC probabilities for at least
4 inches of snow Day 3 are moderate (40-70%) over northeastern
portions of the U.P. along the Lake Superior shore.


...Pacific Northwest through the Northern Rockies...
Days 1-2... 

Moderate atmospheric river PW anomalies of +1 to +2 sigma arrive
into WA/OR this evening as snow levels rise to over 6000ft by
Sunday in this warm core flow. Snow at some Cascades passes this
evening will change to rain through the overnight hours as the
surface cold front eventually moves onshore and height falls
progress inland, spreading snow out of eastern WA/OR and into
northern/central ID, western MT, and western WY from Sunday into
Monday. Exiting upper jet will help with frontolysis and the snow
footprint will largely dissipate by Tuesday morning over the
northern Rockies. WPC probabilities for at least 8 inches of snow
over the next two days are high (>70%) generally above 5000-6000ft
from the WA Cascades to the Blue Mountains, Salmon River,
Sawtooth, Bitterroots, and western WY ranges.


...Central Appalachians through the Interior Northeast...
Day 2...

Multi-stream positively-tilted trough over the Midwest-to-southern
Plains on Sunday will transition to neutral then negative tilt by
Monday morning over the East Coast in concert with an increasingly
buckled S-shaped upper jet over southeastern Canada. Slowing
surface front on Sunday will spur a wave in the Mid-Atlantic that
lifts north-northeastward across southeastern New England early
Monday in the RRQ of the 130kt jet, promoting deepening thereafter
into eastern Maine and into Quebec that afternoon. Strong CAA
behind the front amid a sufficiently moist column will turn rain
to snow from west to east over the central Appalachians into NYS
late Sunday into Monday, especially in elevations above 500-1000ft
(and NW of I-95). Strong NW-tilted FGEN band from NEPA into
northern New England will support snow rates >1"/hr as the rain
changes to heavy, wet snow (high snow load) especially from the
Catskills into the Adirondacks and Green Mountains. There, WPC
probabilities for at least 4 inches of snow are high (>70%) and
for at least 8 inches are moderate (30-70%). Low probabilities
(10-40%) extend farther east into northwestern Maine, southward
into the Berkshires, and westward back through much of central NY
and northeastern PA. Though the system will be progressive despite
the negative tilt, minor fluctuations in the track of the
front/low, speed of incoming cold air (rate of changeover), and
precipitation focus may lead to large changes in the snowfall
amounts. Lake effect snow off Erie and especially Ontario will
persist on Monday with additional accumulation in the Tug Hill.

Farther south, higher elevations of the central Appalachians will
a changeover sooner, and a heavy/wet snow will also accumulate
several inches before ending on Monday. WPC probabilities for at
least 4 inches of snow are moderate (40-70%) over eastern WV into
western MD with slightly lower probabilities into the Blue Ridge.
Both areas have a larger than normal upside potential depending on
how quickly rain can change to snow in light of available QPF.


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