Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EST Sat Feb 16 2019

Valid 12Z Sat Feb 16 2019 - 12Z Tue Feb 19 2019


...Western U.S....

Shortwave energy dropping into the backside of a broad upper
trough centered over the western U.S. is expected to produce
additional periods of snow, with locally heavy accumulations
possible from the southern Cascades to the coastal ranges of
northwest California, as well as the Sierra on Saturday into early
Sunday.  This energy will continue to drop south, introducing the
threat for locally heavy snows into the mountains of Southern
California, the Southwest and the southern Great Basin late Sunday
into early Monday.  By late Monday into early Tuesday, with the
mean trough shifting east, the threat for locally heavy
accumulations is forecast reach into the southern Rockies,
particularly the southern Colorado and northern New Mexico ranges.

...Northern Plains to the lower Missouri valley...

Models continue to show a mid level center developing over the
northern High Plains as energy over the northern Rockies, assumes
a negative tilt while moving farther east later today.  Strong low
to mid level convergence northwest of the center, along with
favorable upper forcing is expected to produce a stripe of
significant snows from eastern Montana into the Dakotas beginning
later today and continuing into Sunday, with WPC Day 1
probabilities (ending 12Z Sunday) showing a High Risk for
accumulations of 4-inches or more from southeast Montana and
southwest North Dakota to central South Dakota.  Meanwhile, more
southerly energy moving east of the central Rockies will
contribute to an area of light to moderate snows moving from the
central Plains into the lower Missouri valley.  WPC Day 1
probabilities show a Moderate Risk for accumulations of 4-inches
or more extending from the Nebraska-Iowa border into central Iowa.

...Great Lakes/Ohio Valley/Northeast...

Energy over the Plains and Midwest on Sunday will become embedded
within increasingly confluent/progressive flow over the eastern
U.S., deamplifying as it moves quickly across through the Ohio
valley into the Northeast late Sunday into early Monday.  Broad
low level theta-e advection and frontogenesis will support a
stripe of generally light snow amounts from the southern Great
Lakes region to southern New England, with a wintry mix farther to
the south across portions of the Ohio valley into the central
Appalachians and northern Mid Atlantic late Sunday into early
Monday.  As shown by the WPC probabilities, widespread heavy snow
or ice accumulations are not expected.

Pereira