Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 PM EST Mon Nov 29 2021

Valid 00Z Tue Nov 30 2021 - 00Z Fri Dec 03 2021


...Great Lakes/Northeast...
Days 1-3...
A clipper system moving across the Upper Midwest this afternoon is
expected to continue to slide quickly to the southeast, moving
across the northern Great Lakes later this evening.  The 12Z
models have shown an upward trend in QPF and snowfall
accumulations as the system impacts Lower Michigan this evening. 
Given the progressive nature of the system, widespread heavy
totals are not expected; however, several guidance members suggest
low-to-mid level frontogenesis may contribute to a short period of
significant snowfall rates between 01-04Z.  Reflecting this trend,
WPC PWPF probabilities for 2 inches or snow have increased notably
across parts of Lower Michigan, with the highest probabilities
centered over central Lower Michigan southeastward into
southeastern Michigan.  This system is expected to spread light
snow into the upper Ohio Valley and the central Appalachians
overnight, with the WPC probabilities indicating little threat for
widespread amounts exceeding 2 inches across the region. 

A more northerly system that is forecast to move north of the
Great Lakes and across southeastern Canada is expected to bring
some warm advection snows to the higher elevations of the Tug Hill
and Adirondacks Tuesday evening.  This along with a period of lake
effect behind the trailing cold front overnight into early
Wednesday may produce a very localized threat for significant
accumulations to the Tug Hill.  WPC Day 2 probabilities - ending
00Z Thu - for snowfall accumulations of 4 inches or more are up to
40 percent across the region.

Meanwhile, another system is expected to drop southeast across
central Canada, supporting mostly light precipitation in the form
of snow changing to rain in many locations across northern
Minnesota, Wisconsin, and Michigan on Wednesday.    The system is
forecast to turn the east, tracking across southern Ontario and
Quebec on Thursday.  Warm advection precipitation is forecast to
spread across the Northeast with a wintry mix at the onset for the
interior, before a change to rain for most locations. However,
thermal profiles may support mostly snow across the Adirondacks,
with WPC probabilities indicating a significant threat for
accumulations of 4 inches or more across the region during the Day
3 period.

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

Pereira