Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 PM EST Mon Feb 25 2019

Valid 00Z Tue Feb 26 2019 - 00Z Fri Mar 01 2019


...Pacific Northwest/California to the Northern Rockies...

An active pattern is forecast to continue, with several additional
feet of snow possible for portions of Sierra and northern Rockies
through the middle portion of the week. 

An upper low centered along the Washington-British Columbia border
is expected to weaken, with energy ejecting east along the
U.S./Canada border on Tuesday.  However, a second low is forecast
to quickly redevelop off of the Pacific Northwest coast on
Tuesday.  Deep onshore flow south of the centers will continue to
usher ample moisture onshore into an west-east oriented low-mid
baroclinic zone.  This along with orographic effects is expected
to support additional heavy snows from the southern Cascades into
the northern Sierra, as well as across the central Idaho to
western Wyoming ranges.  WPC Day 1 probabilities (ending 00Z
Wednesday) indicate a High Risk for additional amounts of a foot
or more for portions of the these areas.

With an upper low remaining anchored off of the Washington-Oregon
coasts, models show a well-defined shortwave moving inland south
of the low into Northern California Wednesday morning. 
Accompanied by a fresh surge of Pacific moisture, this system is
expected to support additional heavy snows, with WPC Day 2
probabilities (ending 00Z Thursday) once again indicating a High
Risk for accumulations of a foot or more across many of the same
Day 1 areas.

Even further additional heavy amounts are possible into Thursday
as the upper low and its associated band begin to move inland.

For the three day period ending 00Z Fri, WPC probabilities are 50
percent or greater for amounts exceeding 30 inches across a large
portion of the Sierra, as well as portions of the Sawtooth in
central Idaho and the Tetons in western Wyoming.

...Great Lakes...

Shortwave energy associated with the remnants of the previously
highlighted low over the Northwest on Day 1, along with a low-mid
level baroclinic zone are expected to support a stripe of mainly
light amounts across the Great Lakes during the Day 2 period,
before shifting farther east into the Northeast on Day 3.

Pereira