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

Valid 12Z Thu Dec 13 2018 - 12Z Sun Dec 16 2018


...Pacific Northwest to the Northern Rockies...
Ongoing heavy snow in the north Cascades and the Olympics is
expected to wane by late today 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 currently over the Rockies will close
into a low over north-central TX today and drift east to LA
through Friday morning. 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 this afternoon into the overnight.
Dynamic cooling should be sufficient for a changeover from rain to
snow at least for higher elevations under the trowal with
nightfall occurring with the heaviest precip late today. While
warm boundary layer conditions will likely limit accumulations,
especially at the onset, precipitation rates look to be sufficient
for at least a few inches of snow, especially across grassy and
elevated surfaces from the northern Concho valley and Northwest
Texas eastward into the northern Hill County and western portions
of Northeast Texas. WPC probabilities for four inches have
increased with moderate-high probabilities now along I-20 west
from Abilene which has higher elevation than surrounding areas.
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.

Jackson