Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 PM EST Tue Jan 01 2019

Valid 00Z Wed Jan 02 2019 - 00Z Sat Jan 05 2019

...Southwest...

An anomalously deep upper low will continue to evolve and move
east across Arizona and New Mexico late Tuesday into Wednesday. 
The 12Z model runs have backed off some, but there remains a good
signal for significant snow accumulations across the southeast
Arizona into the southwest New Mexico ranges.  Strong upper
forcing head of the low, along with enhanced low level convergence
is expected to support locally heavier totals across this region,
with WPC Day 1 probabilities (ending 00Z Thu) indicating the
potential for local amounts of 8-inches across portions of the
region.

...Southern Plains...

As the previously noted upper low continues to move east into the
Southern Plains on Thursday, consensus of the 12Z models was a
little slower/further south than previous runs, with significant
impacts on the expected areas of heavier snow/ice.  While further
adjustments may be forthcoming, 12Z guidance showed the greatest
threat for heavier snow shifting further southwest into southwest
Oklahoma and Northwest Texas and the southern Texas Panhandle. 
WPC Day 2 probabilities (ending 00Z Fri) indicate a Moderate Risk
for 4-inches and Slight Risk for 8-inches or more across this
area.  An icy transition zone is forecast further to the east,
with light to moderate ice accumulations from Northwest Texas to
central Oklahoma.  WPC Day 2 probabilities show a Slight Risk for
ice accumulations of 0.25-inch or more across this area.  The 12Z
guidance backed off on snow/ice amounts further east, with warm
air advection ahead of the low limiting snow/ice accumulations
across eastern Oklahoma into western Arkansas and southern
Missouri.

...Pacific Northwest...

Heavy snow potential is expected to increase across the northern
Cascades beginning Thursday as a deep low approaches the British
Columbia coast.  Snow levels will remain high, limiting the threat
for heavy accumulations mainly to the northern Cascades through
Day 2.  As the low weakens and energy shears inland across western
Canada and the Pacific Northwest, drawing the trailing cold front
further south, snow levels are expected to come down -- extending
the heavy snow threat further south along the Cascades before
precipitation wanes on Friday.

Pereira