Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Mon Nov 04 2019

Valid 12Z Mon Nov 04 2019 - 12Z Thu Nov 07 2019

...Northern Rockies...
Day 1...

Radar shows clusters of valley showers/mountain snow showers
moving northwest to southeast across western to southern MT east
of the sfc frontal boundary, and under the right entrance region
of the upper jet. The upper jet and low level front and enhanced
lift will drift east today and across eastern MT tonight, with
drying aloft over western to south central MT leading to
decreasing snow coverage/intensity. Upslope enhancement leads to
additional light snow in the high terrain of the Big Horns,
Absarokas, BearTooth, and Crazy Mountains. In these ranges, WPC
probabilities are high for 4 inches .

Days 2/3...

A shortwave dropping from Alberta into the Northern Plains will
graze the region Wednesday, driving a cold front south across MT. 
A band of enhanced moisture and brief period of ascent is expected
near the front, producing snow where the moisture and loft
overlap.  and modest right rear quad diffluence in the presence of
a jet streak racing southeastward. This will lead to light
snowfall in the higher terrain of the Lewis Range of MT, but
amounts look to be mostly in the 1-3 inch range.


...Northern Plains/Upper Midwest/Great Lakes...

Day 2/3...

A shortwave dropping through the longwave trough across the east
will spawn weak cyclogenesis moving from NE Tue to near the IA/WI
border Wed morning and then across northern MI into Ontario. This
low will be accompanied by strong right rear quad  diffluence to
enhance ascent, and modest 700-600mb frontogenesis to produce a
band of snowfall from MN into WI and MI. This feature will move
quickly so total snowfall should be limited.

Additionally, prolonged NW flow within the persistent longwave
trough will drive periods of lake effect snow (LES), mostly
downwind of Superior and northern Lake Michigan, where fetch is
sufficient to develop LES banding.
Snow showers off the Lakes into the U.P. and northern portions of
the L.P. of MI will occur on and off through the entire forecast
period (D1-D3), and WPC probabilities are moderate for 4 inches
for the 72-hr period.

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

Petersen