Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 PM EST Thu Dec 13 2018

Valid 00Z Fri Dec 14 2018 - 00Z Mon Dec 17 2018


...Pacific Northwest to the Northern Rockies...
On-going heavy snow in the north Cascades and the Olympics is
expected to wane by this evening as a shortwave ridge begins to
build and snow levels rise ahead of the next shortwave trough.
This next system is forecast to move quickly across the Northwest
late Friday into Saturday. Limited moisture and the progressive
nature of this system are expected to curb the potential for
widespread heavy snow accumulations for Day 2.

A deep low toward the Gulf of Alaska brings the next round of
precip to the Pac NW late Saturday, though the tropically sourced
moisture will have rather high snow elevations associated with it.


...Southern Plains...
A northern stream trough has dropped southeast during the day and
was in the process of closing off a low as it moved across
West/Northern Texas this afternoon. Strong deformation aloft with
low to mid-level frontogenesis is expected to support development
of a narrow stripe of heavier precipitation north/west of the low
as it moves across North Texas, with enough dynamic cooling to be
sufficient to support a changeover from rain to snow at least for
higher elevations under the trowal with nightfall.  Warm boundary
layer conditions will likely limit accumulations, especially at
the onset, precipitation rates look to be sufficient for at least
a couple inches of snow, especially across grassy and elevated
surfaces from the northern Concho valley eastward into the
northern Hill County and a small portion of adjacent plains. 
Agree with the previous forecaster concerning the best chances for
heaviest snow to occur over the higher terrain...generally west of
Abeline...although that threat should be mostly confined early in
the Day 1 forecast period.  Should precipitation rates be high
enough, snow may accumulate in more of a typical band swath rather
than only the highest points under the band.

The probability of significant icing (0.25 inch or more) is less
than percent.

Bann