Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 PM EST Wed Jan 01 2020

Valid 00Z Thu Jan 02 2020 - 00Z Sun Jan 05 2020

Days 1-3...

...Pacific Northwest through the Northern and Central Rockies...
Mid-level energy and strong divergence along the leading edge of a
powerful upper jet will continue to support areas of organized
precipitation, including high elevation snows, across the
Northwest into the northern Great Basin and the northern and
central Rockies through Wednesday evening.  While upstream energy
is forecast to support snow showers into early Thursday, expect
precipitation to diminish across most areas as the upper trough
shifts east and a strong ridge begins to build along the West
Coast by late Thursday. 

A warm front lifting across the region is forecast to bring
additional snows to the high elevations of the northern Cascades,
while most other areas remain dry on Friday.  Then by early
Saturday, another upper level shortwave and associated cold front
are expected to move across the Northwest, delivering more
widespread snows to the Olympics, Cascades and northern Rockies.

...Ohio Valley to the Lower Great Lakes...
The previously noted trough in the West is forecast to move east
into the Plains on Friday, with southern stream energy lifting
north through Ohio valley ahead of an amplifying northern stream
trough over the northern Plains and upper Midwest.  Deepening cold
air may support rain changing to snow behind an area of low
pressure lifting through the Ohio valley toward the Lower Great
Lakes on Saturday.  However, models differ significantly on the
degree of phasing and the timing of this system -- greatly
limiting forecast confidence.


For Days 1-3, the probability of significant icing (0.25 inches or
more) is less than 10 percent.

Pereira