Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
440 PM EST Fri Dec 13 2019

Valid 00Z Sat Dec 14 2019 - 00Z Tue Dec 17 2019


Days 1-3...

...Western U.S....
Mid-level energy embedded within progressive, westerly flow will
continue to promote periods of organized heavier snow in the
mountains from the Sierra to the central Rockies.  Areas expected
to more significantly impacted through into Saturday include the
Sierra, the mountains of northeastern Nevada, the western and far
south-central Wyoming ranges, the northern and central Utah and
the western Colorado ranges.

On Sunday, the mid-to-upper level pattern is expected to amplify
with a mid-level shortwave/upper jet diving southeast across
California into the Great Basin.  This will support light to
moderate snow accumulations farther south across southern Utah
into northern Arizona, with heavy amounts more likely across the
San Juan and Sangre de Cristo mountains in southern Colorado and
far northern New Mexico.

...Central Plains to the Ohio Valley...
As the previously noted shortwave begins to move east across the
Rockies into the High Plains, models show a stripe of warm
advection precipitation developing and extending east from the
central Plains into the mid Mississippi valley on Sunday.  Thermal
profiles suggest mainly snow across northern Kansas eastward
across northern Missouri, southern Iowa and central Illinois, with
a wintry mix farther south on Sunday.

As the upper level trough continues to move east Sunday night into
Monday, warm advection precipitation consisting a of a wintry mix
is forecast to shift east from the Mississippi through the Ohio
valley into the Appalachians.  Meanwhile, additional snows will
develop on the backside of a deepening surface low as it tracks
from the mid Mississippi into the Ohio valley on Monday.

...Lower Great Lakes...
A southern stream mid level trough moving from the lower
Mississippi valley into the Southeast will begin to interact with
a northern stream trough digging into the upper Midwest --
assuming a negative tilt as it lifts north along along the East
Coast on Saturday.  A rapidly developing surface cyclone will
track from the Mid Atlantic across the Northeast late Saturday
into Sunday.  While mostly rain is expected ahead of the system,
strong cold air advection on the backside of the departing low
support lake effect snow showers, with locally heavy amounts
developing in the of the of the Lower Great Lakes on Sunday.

Pereira