Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EST Thu Feb 09 2023

Valid 12Z Thu Feb 09 2023 - 12Z Sun Feb 12 2023

...Corn Belt/Upper Midwest/Great Lakes and Northeast...
Day 1...

Compact closed mid-level low at the entrance region of a short
anticyclonically-curved upper jet across the Great Lakes will lift
northeastward today as a surface low moves from IL to MI to
Ontario by this evening. Moisture surge (WCB) out of the central
Gulf will wrap into the occluded system and a deformation band on
the northwest side of the low will move northeastward in tandem
with the surface low with snowfall exceeding 1"/hr per the CAM
guidance/WPC Snowband Probability Tracker page. Temperatures are
marginal but the column will cool especially where strong UVV
turns rain to snow. Guidance shifted a bit southeast with the
overall QPF footprint, and nudged the forecast in this way as
well. Lots of spread exists in the guidance which depends upon the
strength of banding and amount of cooling relative to the max QPF
axis, but a band of >6" of snow is likely over portions of eastern
IA into south central WI. WPC probabilities of at least 4 inches
of snow are moderate (>40%) along the MS River between IA/IL
northeastward across southern WI and into northern Lower Michigan.
This afternoon into tonight/early Friday, WAA-driven precip will
overspread northern NY/New England as the warm front lifts into
the area. Temperatures are cold here and areas that are slow to
warm may see a period of freezing rain with some accumulation over
a tenth of an inch. Snow will turn to rain from south to north,
remaining nearly all snow only over far northern Maine near the
Canadian border. System will lose favorable upper dynamics as the
triple point takes over just off the coast and drags the rest of
the system with it by the start of D2. WPC probabilities of at
least 4 inches of snow are high (>70%) over the northern 1/3 of
Maine. Light lake effect snow will follow behind the exiting
system for 18-24 hours favoring the typical NW-flow regions in the
U.P. and into the Tug Hill.


...West...
Days 1-3...

Upper trough south of the Gulf of Alaska will carry a cold front
into the Pac NW this evening with a modest surge in moisture on
SSW to S flow. Snow levels will lower from around 4000ft to near
3000ft as the front moves ashore and heights lower. The most
appreciable snow will be in the higher terrain of the Cascades and
Olympics. By D2, incoming trough will split, pinching off a closed
low over NorCal as snow ends over WA. QPF will be on the light
side, and snow will accumulate to only a few inches except for the
northern WA Cascades. By D3, closed low will drop southward along
the CA coast, limiting snowfall to the Sierra where only a few
inches are forecast. WPC probabilities for more than 4 inches each
day are low in CA (<40%) but high over the WA Cascades.


...Southern Appalachians...
Day 3...

Trailing shortwave on the southwest side of the broader longwave
trough D1 over the Plains will move through TexArKana D2 well
northwest of the cold front associated with the D1 system
lingering in the Gulf. Light snow is forecast for portions of the
Ozarks into southern MO but WPC probabilities for more than 4
inches are less than 10 percent. As the system moves eastward on
D3, an area of low pressure may form along the front near the FL
Panhandle and lift northeastward as the cold upper low moves into
the Southern Appalachians. Temperatures over the area will be
elevation-dependent, but parts of the Smokeys may see several
inches of snow by early Sunday, continuing into D4. Through 12Z
Sunday, WPC probabilities of at least 4 inches of snow are low
(10-20%).



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