Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
236 AM EST Sat Nov 20 2021

Valid 12Z Sat Nov 20 2021 - 12Z Tue Nov 23 2021

...Great Lakes...
Days 2-3...

A shortwave trough embedded within progressive northwest flow over
western Canada this morning is expected to dive across central
Canada, amplifying as it approaches the Upper Midwest Sunday
morning.  This feature is forecast to swing east, with several
models showing a compact upper low developing as it moves across
the northern Great Lakes Sunday night.  A surface low is expected
to quickly develop north of the lakes and move northeast from
northern Ontario into Quebec.  Strong cold air advection provided
by deep northwesterly flow on the backside of the system will
support lake effect snow showers developing initially off of Lake
Superior into the U.P. and northern Lower Michigan, where locally
heavy amounts may accumulate beginning Sunday and continuing into
Monday.  By Monday night and continuing into early Tuesday, flow
will support lake effect showers east and southeast of lakes Erie
and Ontario.  Activity is expected to wane as deep ridging shifts
east across the Lakes on Tuesday.

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

Pereira