Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
234 PM EST Wed Dec 11 2019

Valid 00Z Thu Dec 12 2019 - 00Z Sun Dec 15 2019


Day 1...

...Northern Plains to the Upper Great Lakes...
A mid-level shortwave will continue to drop southeast from western
Canada into the northern Plains Wednesday evening.  Models show
this fast-moving system producing light snow accumulations as it
tracks from eastern Montana across North Dakota and eastern South
Dakota overnight.  Then on Thursday, models continue to show
low-to-mid level frontogenesis along with right-entrance region
upper jet forcing supporting a period of enhanced snowfall,
raising the potential for heavier totals across portions of the
Upper Great Lakes region.  Latest WPC guidance shows greater than
50 percent probabilities for 24-hr totals of 4-inches or more
across parts of northern Wisconsin and the Upper Peninsula of
Michigan.

...Pacific Northwest to the Northern Rockies...
Shortwave ridging is forecast to give way to fast Pacific flow. 
Embedded shortwave energy and deeper moisture is expected to
support periods of heavy mountain snow across the Cascades and the
northern Rockies beginning Wednesday evening and continuing into
Thursday.  Areas impacted by heavy snow accumulations (8-inches or
more) through late Thursday will likely include portions of the
Cascades and the Idaho and western Wyoming Rockies.

Day 2...

...Northern Plains and Upper Midwest...
A second shortwave trough is forecast to impact the region on
Friday.  This system is expected to track farther to the north,
with less potential for heavier amounts.  WPC probabilities show
the best chance for accumulating snow centered over northeastern
North Dakota into northwestern Minnesota.  However, WPC
probabilities for amounts of 4-inches or more are less than 10
percent across this area.

...Pacific Northwest to the Central Rockies...
Progressive westerly flow will continue to extend across the
western U.S., with heavy snow continuing into Friday for portions
of the Cascades and northern Rockies.  Heavy snows are also
expected to extend farther to the south into the northern Utah and
northern Colorado ranges as well.  WPC probabilities indicate
additional accumulations of 8-inches or more are likely for
portions of the Cascades, as well the Rockies from northern Idaho
and western Montana to northern Utah and northern Colorado.

Day 3...

...Western U.S....
Axis of organized heavier snows will continue to shift south, with
shortwave energy driving a low-to-mid level baroclinic zone
farther south into the the northern Sierra, Great Basin and
central Rockies.  This may support some additional heavy amounts
along the Wasatch, Unitas and the western Colorado ranges. 
Locally heavy amounts are also possible for portions of the
northern Sierra as well as mountains of northern Nevada.

Pereira