Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Tue Feb 26 2019

Valid 00Z Wed Feb 27 2019 - 00Z Sat Mar 02 2019


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

To the south of an upper low anchored off of the the
Washington-Oregon coast, models show a well-defined shortwave
moving inland into southern Oregon and northern California
Wednesday morning.  This will bring a fresh surge of deeper
moisture into a quasi-stationary baroclinic zone extending from
near the Oregon-California border through the northern Rockies. 
This will support additional heavy snows from southern Oregon and
northern California eastward into the northern Rockies through
Tuesday night, with snow spreading farther south along the Sierra
as the upper trough moves inland Wednesday morning.  With
additional amounts of two feet or more possible in some areas, WPC
Day 1 probabilities (ending 00Z Thu) show a High Risk for
accumulations of a foot or more for portions of the California
Cascades and northern Sierra.  WPC probabilities also continue to
indicate a High Risk for a foot or more over the Sawtooth of
central Idaho.

The upper low along the Northwest coast is expected to begin
moving inland on Thursday, with additional heavy snows possible
ahead of the associated wave pushing east from the Pacific
Northwest to the northern Rockies and along the trailing front
extending back into northern California. 

Models show the upper low continuing to weaken through early
Friday, with remnant energy moving east into the northern Plains
ahead of a deep low settling south over central Canada.  This
along with increasing frontogenesis is expected to support a swath
of light to moderate snows from western to southeastern Montana. 
Meanwhile, low amplitude mid level energy and an upper level jet
streak will help to support some locally heavy accumulations
across the Colorado Rockies on Friday.

...Great Lakes/Northeast...

A shortwave trough associated with the remnants from upper low
emanating from the Northwest is expected to quickly move from the
northern Plains and upper Midwest into the Great Lakes on
Wednesday.  Ahead of the wave, increasing low level theta-e
advection into a low-mid level baroclinic band will support a
stripe of light to moderate snows centered across the Great Lakes
on Wednesday, before shifting farther to the east into Upstate New
York and central and southern New England Wednesday night into
Thursday morning.

Pereira