Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
401 AM EST Fri Feb 15 2019

Valid 12Z Fri Feb 15 2019 - 12Z Mon Feb 18 2019


...Western U.S....

An anomalously deep upper low will continue to settle south along
the Washington and Oregon coasts on Friday, supporting another
round of heavy snows for the coastal ranges of northwest
California, as well as the Sierra, before the system weakens and
moves inland Friday night into Saturday.  WPC Day 1 probabilities
(ending 12Z Saturday) show a High Risk for accumulations of
12-inches or more across the interior mountains in northwest
California, in addition to a large portion of the Sierra. 
Trailing energy diving south along the coast will continue to
maintain below normal heights and additional periods of snow,
producing localized heavy totals for portions of southwest Oregon
and Northern California into early Sunday.  By late Sunday, models
show the upper trough beginning to shift farther to the southeast,
with surface high pressure extending south across the Northwest. 
Shortwave energy moving through the base of the trough is expected
to support some localized heavy amounts from the coastal ranges of
Southern California to the southern Rockies, including the higher
elevations of the Southwest and the southern Great Basin. 
However, limited moisture is expected to hamper the threat for
widespread heavy accumulations.

...Central Plains and Ozarks to the lower Ohio valley...

A low-amplitude shortwave moving east of the Rockies is expected
to produce widespread light to moderate precipitation along and
north of frontal boundary extending from Tennessee valley back
into the southern Plains on Friday.  Shallow cold air north of the
front will support a wintry mix, with WPC Day 1 probabilities
maintaining a Moderate Risk for ice accumulations of 0.25 inch or
more centered along the Missouri-Arkansas border into the lower
Ohio valley.  Farther to the north and within the deeper cold air,
significant snow accumulations are more likely, with WPC
probabilities showing a Moderate Risk for snow amounts of 4-inches
or more from the eastern Nebraska-Kansas border across central
Missouri on Day 1.

...Northern Rockies and Plains...

Energy ejecting out ahead of the low in the West will support
additional periods of snow as it moves east across the northern
Rockies late Friday into early Saturday.  As the energy moves
farther to the east on Saturday, expect light to moderate snows to
develop north and west of low-mid level center closing off over
South Dakota-Nebraska on Saturday.  WPC Day 2 probabilities
(ending 12Z Sunday) shows a Moderate Risk for accumulations of
4-inches or more extending from southwest Montana to central South
Dakota.

...Northeast...

A deepening low over the Great Lakes will continue to track to the
northeast on Friday.  Warm advection precipitation east of the low
will begin as snow, with some significant accumulations possible
for portions of interior northern New England before precipitation
transitions to rain Friday evening.

Pereira