Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Sat Nov 09 2019

Valid 12Z Sat Nov 09 2019 - 12Z Tue Nov 12 2019


...Northern Plains and Rockies...
Days 1-2...

Combination of a southward sinking arctic cold front and a jet
streak racing across from Montana into the Western Great Lakes
will enhance ascent today into Sunday. In addition, post frontal
upslope flow and modest mid-level fgen will drive a stripe of
light to moderate snowfall oriented NW to SE from near Glacier NP
into Iowa. Although the intensity and duration of snowfall is
expected to be limited, pockets of heavy snowfall are likely in
the terrain of MT and WY, as well as into the Black Hills of SD,
where WPC probabilities are greater than 50% for 4 inches, and
could exceed 8 inches in the highest peaks.


...Great Lakes...
Days 1-3...

An upper level trough remaining, and amplifying, across the east
will persist a setup favorable for Lake Effect snows through early
next week. Modest snow is possible today and Sunday as sfc-700mb
temperature differential is moderate and directional shear is
significant. However, by day 3 /Monday/ strong CAA will rapidly
steepen the lapse rates and deepen the inversion while maintaining
a saturated DGZ. Additionally, flow becomes more unidirectional
from the N/NW and intensifies, and the environment looks to become
extremely favorable for heavy LES in the favorable N/NW snow belts
Monday. After modest accumulations D1-D2, WPC probabilities
feature a high risk for 6+ inches in the eastern U.P. and W/NW
portions of the L.P. of MI. Snow rates during Monday may also
become more intense, and the potential exists for convective snow
bands late in the forecast period which could create locally much
higher snowfall accumulations.


...Northeast...
Day 3...
Wave of low pressure developing along a cold front and in response
to modest mid-level forcing will move progressively northeastward
from the Ohio Valley. The guidance has become subtly more
amplified with the upper trough allowing the surface low to move
inland of the major cities from Philadelphia, PA through Boston,
MA, keeping the airmass cold enough for snow confined to inland
portions of New York and New England. Although the system is
expected to be progressive, a prolonged period of modest 850-600mb
fgen will likely produce a swath of moderate to heavy snow from
the Adirondacks of NY through the Green and White mountains of New
England. The heaviest snowfall is likely in the highest terrain
where upslope enhancement is likely, and WPC probabilities are
high for 6 inches in portions of the Adirondacks, as well as the
highest terrain of VT and NH. Locally 12" is possible in the
highest peaks. Further SE into the foothills and towards the
coast, WAA will make the column too warm for snow until the low
pulls away and CAA commences. Some light freezing rain is possible
before changeover to snow occurs, but accumulations of snow and/or
freezing rain should be light through 12Z Tuesday.

The probability for significant icing is less than 10 percent all
3 days.

Weiss