Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 PM EST Mon Jan 17 2022

Valid 00Z Tue Jan 18 2022 - 00Z Fri Jan 21 2022

...Northeast/central Appalachians...
Day 1...

Cyclonic circulation around the departing deep surface low will
continue to support lake-effect and upslope snow via northwesterly
winds, including into the central Appalachians. Localized amounts
near 4 inches are possible this evening before snow showers taper
off on Tuesday.


...Upper Midwest through the Great Lakes...
Days 1-3...

A clipper system will dive southeast out of Alberta and then move
along and just south of the US/Canada border into the Great Lakes
before lifting off into Ontario by D3. While this system is
fast-moving and has limited total forcing associated with it, some
modest WAA will enhance moisture and squeeze out a swath of
moderate to heavy snow across northern MN, northern WI, and the
U.P. of MI where WPC probabilities are high for 4+ inches and
locally more than 6 inches is possible. Guidance has ticked down a
bit again across northern MN as have NBM 90th percentile values.

On D2, cyclonic flow on the backside of the surface low along with
CAA across the Great Lakes will support some LES in the favored
N/NW snow belts, especially downwind of Lake Superior and Lake
Michigan. The airmass is quite cold behind this system (850T
around -24C and sfc Ts around -10 to -15C), which will limit SLRs
a bit beyond the favorable DGZ range. As strong high pressure
slips into the Dakotas/Minnesota D3 (mid 1040s mb), flow will
become rather northerly across the western lakes favoring lighter
multi-bands over the U.P but perhaps a bit more concentrated band
into extreme SW Lower MI and northwestern IN.

WPC probabilities are moderate to high for more than 4 inches
across portions of the U.P. and western Lower MI. Three-day totals
over 6 inches are likely in favored U.P. areas.


For days 1-3, the probability of significant icing is less than 10
percent.


Fracasso/Weiss