Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Sun Nov 03 2019

Valid 12Z Sun Nov 03 2019 - 12Z Wed Nov 06 2019

...Great Lakes...

Days 1-3...

On Sunday, lake-enhanced snow bands will become more widespread
over the favored west-flow LES snowbelts downwind from Lake
Ontario. Probabilities of 4+ inches of snow will be highest over
the elevated terrain in the Tug Hill Plateau (over 50%), with
potential for several inches of snow.  

LES bands will become more scattered Sun morning in the upper
lakes given the loss of synoptic enhancement as the shortwave
pivots eastward. The overall light QPF (generally under 0.25")
will keep probabilities of exceeding 4 inches under 30% per the
multi-model ensemble suite -- again focused over the relatively
more elevated terrain farther inland from Lakes Superior and
Michigan.

Mon-early Tue...additional shortwave energy pivoting through the
base of the longwave trough will generate more lake enhanced
snowfall across the Great Lakes, especially outside of peak
diurnal heating (Mon morning and again Mon night-Tue morning). 48
hour probabilities of at 2-4" will be highest across the Huron and
Porcupine mountains in western Upper MI, along with the the more
elevated terrain (over 1200') in nw-nc Lower MI.  The next wave
arrives Tue night with modest synoptic scale lift in advance of a
700 mb trough crossing the upper MS Valley.  

...Northern Rockies/Northern Plains/Upper MS Valley...

Days 1-2...
Mid-upper level shortwave energy (and higher RHs) on the back side
of the longwave trough, in conjunction with the upslope easterly
flow at lower levels, will favor moderate upslope snow behind the
low level cold front across the mountains in northern WY into
central MT. Highest 48 hr (2-day) probabilities of exceeding 4" 
were noted over the northern Big Horns, in the Absaroka range, and
across the Crazy and Big Snowy mountains in central MT. Snow
diminishes as the band of confluent flow and lift shifts east into
eastern MT and WY.

Day 3...
A defined 700 mb wave is forecast to enter the Northern Plains Tue
morning and progress steadily downstream across the region and
then across the upper MS valley, arriving in the upper Great Lakes
Wed morning. In tandem with the wave is expected to be a band of
enhanced moisture and lift, resulting in a period of snow that
lasts several hours before ending as the wave passes and moves
downstream.  Given the progressive wave and limited duration of
snow, probabilities for heavy snow are low.

The probability of significant icing (0.25 inches) is less than 10
percent all 3 days.

Petersen