Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 PM EST Mon Nov 30 2020

Valid 00Z Tue Dec 01 2020 - 00Z Fri Dec 04 2020



...Ohio Valley/Great Lakes/Central to Southern Appalachians...
Days 1-3...
Not much change to the forecast as models continue to signal a
significant lake-effect/orographic snow event in the lee of the
eastern Great Lakes this period. 

Phasing streams over the Ohio valley will support a deepening low
that is forecast to lift north from the Ohio valley into the
eastern Great Lakes by early Tuesday.

Rain changing to snow is already occurring across much of the Ohio
valley and will continue as cold air spreads around the backside
of the strengthening system.  As the system continues to intensify
and lift north, areas south of Lake Erie will become likely areas
for heavy snowfall.  Synoptic scale ascent, combined with a lake
effect moisture channel extending from Lake Huron, will support
long duration heavy snow from north-central Ohio to western New
York.  WPC PWPF suggests accumulations of 8-inches or more will be
common, with locally heavier totals likely (especially across
northeastern Ohio, including the Cleveland metro) through Tuesday
night.

As the low pulls further north late Tuesday into Wednesday, snows
are expected to develop east of Lake Ontario in the Tug Hill, with
moderate accumulations forecast.  Several inches of snow are
expected before the low departs Wed.

Meanwhile, moist, cold, northwest flow will lead to periods of
snow in the favored upslope regions along the North
Carolina/Tennessee border.  From western Pennsylvania to Western
Virgnia, northwest flow will carry lake moisture south --
supporting periods of snow, with several inches possible along the
favored upslope terrain through early Wednesday.

...Southern to South Central Plains...
Days 2-3...
The models show an elongated north-south 850-700 mb trough
extending down the plains on Wed. The models show a closed low
likely forming in the base of the trough somewhere in the southern
Plains.  Lift occurring in the cold sector of the low has the
potential to bring snow to portions of western-central Kansas and
Oklahoma Wednesday into early Thursday.  Differences in the track
and intensity of the system continue to limit forecast confidence
with this system.  However, this system does have the potential to
bring amounts more significant than the low WPC PWPF probabilities
suggest.

For Days 1-3, the probability of significant icing (0.25 inch or
greater) is less than 10 percent.

Pereira