Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
402 PM EST Sat Jan 11 2020

Valid 00Z Sun Jan 12 2020 - 00Z Wed Jan 15 2020


Days 1-3...

...Western Great Lakes...
Ongoing freezing rain will continue into the evening hours, with
additional ice accumulations of 0.10-inch or more possible across
southeastern portions of Lower Michigan before ending as a brief
period of snow Saturday night.  Meanwhile, a mid-upper level
shortwave associated with a surface low over the lower Ohio Valley
will continue to assume a negative tilt as it lifts across the mid
Mississippi valley Saturday evening.  Increasing low-to-mid level
frontogenesis, in addition to the increase in upper level forcing,
will support moderate to heavy snows developing northwest of the
surface low as it moves from the Ohio Valley into the Great Lakes
region Saturday evening.  WPC PWPF shows that snow accumulations
of 6-inches or more are most likely across portions of northern
Lower Michigan.

...Northeast...
As cold high pressure remains locked in place to the north, low
pressure lifting into the Great Lakes region Saturday evening will
slide east on Sunday along a frontal band sagging south through
the St Lawrence valley into the Northeast.  Shallow cold air north
of the boundary will support freezing rain, with significant ice
accumulations likely Saturday night and Sunday morning.  WPC PWPF
continues to indicate that widespread ice accumulations of 0.10 to
0.25-inch, with locally heavier amounts, are likely from the
Thousand Island region of New York to northern Vermont and far
northern New Hampshire and then from the White Mountains in
western Maine to Downeast Maine.  Meanwhile, deeper cold air to
the north will support more sleet and snow, with heavy snow
accumulations possible across northern Aroostook County in Maine.

...Pacific Northwest to the Northern Rockies...
The shortwave trough currently impacting the region will continue
to dig southeast Saturday evening, but be quickly followed by yet
another system diving southeast toward the coast on Sunday.  In
addition to bringing additional heavy snows to the mountains,
colder air accompanying this system will raise the threat for
lowland snows across western Washington by late Sunday.  With snow
levels remaining low, models show another system sliding into the
Northwest on Tuesday.  The potential for heavy snow accumulations
remains high with WPC PWPF indicating high probabilities for
additional accumulations of 2-feet or more across a large portion
of the Cascades.  Locally heavy accumulations are also likely
across the mountains of far southeastern Washington and
northeastern Oregon, as well as the northern and central Idaho and
northwestern Wyoming ranges.

Pereira