Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
426 PM EDT Sat Nov 02 2019

Valid 00Z Sun Nov 03 2019 - 00Z Wed Nov 06 2019


...Great Lakes...

Days 1-3...
As the upper shortwave trough pivots eastward across the Upper
Great Lakes, LES banding with the BL w/wnw flow will become better
organized this evening across portions of Upper and northern Lower
MI given the shortwave interaction (deeper moist CBL). Moreover,
any early-season diurnal effects (disruption of discrete LES bands
over land) should diminish quickly around sunset, while surface
and BL temps falling below 0C farther inland from the lakeshores
will make for more efficient accumulation efficiency.

LES bands will become more scattered late Sat night and Sun
morning 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.

Downwind from Lake Erie and Ontario - in a similar fashion,
lake-enhanced snow bands will become more widespread over the
favored west-flow LES snowbelts later Sat night and through Sun
morning. Probabilities of 4+ inches of snow will be highest over
the elevated terrain in the Tug Hill Plateau (over 50%), with the
multi-model ensemble 50th percentile (i.e. most likely) total
snowfall ranging between 1-2 inches. 

Mon-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 least 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.

...Northern Rockies...

Days 1-3...
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 to locally heavy upslope
snow behind the low level cold front across the mountains in north
central-northwest WY into south-central and central MT. Highest 72
hr (3-day) probabilities of exceeding 8", greater than 50%, were
noted over the northern Big Horn and Absarokas Mountains into
Yellowstone Country of MT and across the Crazy and Big Snowy
mountains in central MT.

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

Hurley