Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
419 PM EST Wed Dec 12 2018

Valid 00Z Thu Dec 13 2018 - 00Z Sun Dec 16 2018


...Pacific Northwest to the Northern Rockies...

The potential for heavy snow is expected to increase once again
Wednesday night into Thursday across the Olympics, northern
Cascades and far northern Rockies as onshore flow amplifies ahead
of shortwave system moving into British Columbia.   WPC Day 1
probabilities (ending 00Z Thursday) indicate amounts of a foot or
more are likely for areas in the northern Washington Cascades
above 4000 ft.

Heavy snow threat is expected to wane by late Thursday as a
shortwave ridge begins to build and snow level 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.

...Southern Plains...

Shortwave trough currently over the Northwest will continue to
amplify, with an anomalously deep center developing as the system
digs southeast into the southern Plains Thursday morning.  Strong
deformation aloft with low to mid level frontogenesis is expected
to support a narrow stripe of heavier precipitation northwest of
the low as it moves across Northeast Texas late Thursday into the
overnight hours.  It is expected that dynamic cooling will be
sufficient for a changeover from rain to snow for some areas. 
While warm boundary layer conditions will likely limit
accumulations, especially at the onset, and hamper the potential
for widespread significant amounts, precipitation rates may 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.

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

Pereira