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

Valid 00Z Mon Nov 04 2019 - 00Z Thu Nov 07 2019

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

A cold front dropping through the Northern Plains will lag back
against the eastern Rockies, leading to low-level upslope flow
from the E/NE. At the same time, a jet streak extending from the
high latitudes of Canada will drop southward placing modest LFQ
diffluence overhead to initiate synoptic lift, while weak impulses
rotate around the longwave trough axis to the east. These features
together will produce snowfall within a narrow ribbon of high
700mb RH, with the upslope enhancement leading to the highest
accumulations in the high terrain of the Big Horns and Absarokas.
In these ranges, WPC probabilities are high for 4 inches, with
lesser amounts likely from the Northern Rockies near Glacier NP,
to as far SE as the Pine Ridge of Nebraska where probabilities for
1" fall below 10%.

Day 3...

A robust shortwave dropping from Alberta into the Northern Plains
will graze the region Wednesday, in conjunction with higher
mid-level RH and modest RRQ diffluence in the presence of a jet
streak racing southeastward. This will lead to renewed snowfall in
the higher terrain of MT, but WPC probabilities for 4" are less
than 20%.

...Upper Midwest/Great Lakes...
Day 3...

A shortwave dropping through the longwave trough across the east
will spawn weak cyclogenesis moving from ND into WI Tuesday into
Wednesday. This feature will be accompanied by strong RRQ
diffluence to enhance ascent, and modest 700-600mb fgen to enhance
a belt of snowfall from MN into WI. This feature will move quickly
so total snowfall should be limited, but WPC probabilities are
high for 2+" in central WI. Additionally, prolonged NW flow within
the persistent longwave trough will drive periods of LES, mostly
downwind of Superior and Michigan where fetch is appropriate 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.

Weiss