Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Mon Jan 20 2020

Valid 12Z Mon Jan 20 2020 - 12Z Thu Jan 23 2020


Days 1-3...

...Western U.S....
Models continue to show widespread precipitation returning to the
West as a frontal band associated with a weakening upper low moves
across the Pacific Northwest and northern California on Tuesday. 
This system is expected to produce locally heavy snows over the
Olympics, Cascades and northern Sierra, with generally lighter
amounts spilling over into the northern Rockies.  A warm front
lifting across the Northwest is expected to bring additional
snows, with locally heavy accumulations across the Olympics and
northern Cascades late Wednesday into early Thursday.

...Ozarks/Mid Mississippi Valley/Upper Great Lakes...
High pressure over the Plains is expected to shift east, setting
up a broad warm advection pattern from the western Gulf of Mexico
to the Upper Great Lakes on Wednesday.  A mid level shortwave
lifting out of the base of the broader scale trough is expected to
support organized, but generally light precipitation from the
Ozarks, lower Missouri and mid Mississippi valleys northeastward
to the Upper Great Lakes Wednesday into early Thursday.  Snow is
expected, at least at the onset, resulting in some light snow
accumulations from the mid Mississippi valley northeastward to the
Upper Great Lakes.  Overall snow accumulations are expected to be
light, with WPC PWPF indicating little threat for widespread
accumulations of 4-inches or more.  Farther to the south, a wintry
mix is more likely, with light ice accumulations possible across
the Ozarks.

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

Pereira