Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
358 PM EST Sun Jan 12 2020

Valid 00Z Mon Jan 13 2020 - 00Z Thu Jan 16 2020


Days 1-3...

...Pacific Northwest to the Northern Rockies...
A well-defined upper level shortwave and its associated frontal
band will continue to move east, producing areas of organized
heavy snow from the Northwest into the northern Rockies Sunday
night.  Colder air behind the front will draw snow levels lower,
bringing snow into the lowlands of the western Washington.  Cold
air will remain in place as the next system moves into the region
by late Monday.  This system is forecast to track farther to the
south than the previous while bringing even colder air into the
Northwest.  In addition to heavy snows along the southern Cascades
and coastal ranges of southwestern Oregon and northwestern
California, significant accumulations are also possible across the
lower elevations of western Oregon as well.  Fast, zonal flow with
embedded mid level energy will support snow showers across the
region through Tuesday into early Wednesday.  As an amplifying
shortwave approaches the coast, organized heavier precipitation is
forecast to return to western Oregon and northwestern California
by late Wednesday.  This is expected to bring additional heavy
accumulations to the coastal ranges and Cascades.  WPC PWPF shows
that three-day totals will likely exceed two feet across a large
extent of the Oregon Cascades, as well as for portions of the
southwestern Oregon and northwestern California coastal ranges.

...Upper Midwest...
A negatively-tilted upper trough will lift from the Plains into
the Upper Midwest, supporting mostly light snow from Minnesota to
Upper Michigan on Tuesday. Low level southeasterly flow ahead of
the system may produce some lake-enhanced heavier totals along the
northwest shore of Lake Superior into the Arrowhead region of
Minnesota Tuesday morning.

The probability of significant icing (0.25-inch or greater) is
less than 10 percent.

Pereira