Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 AM EST Tue Jan 21 2020

Valid 12Z Tue Jan 21 2020 - 12Z Fri Jan 24 2020


Days 1-3...

...Western U.S....
A frontal system approaching the Northwest coast this morning is
expected to move inland on Tuesday, bringing widespread
precipitation, including mountain snows to the Pacific Northwest,
northern California and the northern Rockies.  Areas impacted by
the heaviest snowfall accumulations will likely include the
Olympics and northern Cascades, where WPC PWPF indicates local
accumulations of a foot or more are likely during the Day 1 period
(ending 12Z Wed).  Unsettled conditions are expected to continue
across the Northwest through early Friday.  Models continue to
show a warm front lifting along the coast on Wednesday, followed
by a cold front moving inland late Thursday into early Friday. 
However rising snow levels will confine the threat for heavy snows
primarily to the higher peaks of the Olympics and northern
Cascades.

Meanwhile, a southern stream trough moving into Southern
California Tuesday morning is forecast to move quickly east across
the Southwest and into the southern Rockies later today.  This
will bring accumulating mountain snows, with mainly light amounts
expected from Utah and northern Arizona to western Colorado and
northern New Mexico.

...Southern Plains and Midwest...
Several shortwaves moving through a broader scale trough
developing over the central U.S. are expected to bring widespread,
but mainly light precipitation to the region beginning Wednesday
and continuing into early Friday.

Initial area is expected to develop Tuesday night-Wednesday
morning across the central and southern Plains as the previously
noted shortwave moving across the Southwest translates east of the
Rockies.  Boundary layer temperatures remain marginal, however the
overall trend of the models has been colder, indicating greater
potential for accumulating snows across central to eastern Kansas
Wednesday morning.  Energy moving into the Plains is expected to
begin lifting northeast ahead of a northern stream trough moving
into the northern High Plains on Wednesday.  This will support
light snow and ice spreading northeast from the lower Missouri and
mid Mississippi valleys to the Upper Great Lakes Wednesday into
early Thursday.

As this leading energy moves across the Upper Great Lakes Thursday
morning, additional energy moving through the base of the trough
will foster redeveloping precipitation across eastern Oklahoma
into Arkansas and southern Missouri, where the consensus of the
overnight models showed good potential for freezing rain. 
Meanwhile, as energy from the northern High Plains drops southeast
and an upper low begins to develop over the mid Mississippi
valley, this will support precipitation developing farther north,
with additional snows across the mid Mississippi valley late
Thursday into early Friday.


Pereira