Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
430 PM EST Sat Jan 09 2021

Valid 00Z Sun Jan 10 2021 - 00Z Wed Jan 13 2021


...Southern Rockies to the Lower Mississippi Valley...
Beginning this evening and continuing through Sunday, a winter
storm is likely to produce significant snowfall accumulations
across portions of the southern Rockies and southern Plains.  Then
by late Sunday and continuing into early Monday, the focus is
forecast to shift farther east, with the potential for heavy snow
impacting portions of the lower Mississippi valley.

A shortwave trough digging into the Four Corner region this
afternoon is forecast to swing east into the southern Rockies
later this evening.  Left-exit region upper jet forcing is
expected to help support large-scale lift across the southern
Rockies and High Plains this evening into the overnight.  This
lift along with deepening moisture, supported by low level
southeasterly flow across Texas, will foster an expanding area of
precipitation from the Colorado and northern New Mexico mountains
eastward into the High Plains.  For the evening into the overnight
hours, models are in generally good agreement, showing a weak
mid-level circulation moving east from northeastern New Mexico
into the Panhandle region, supporting some organized heavier rates
across portions of southeastern Colorado and northeastern New
Mexico into the northern Panhandle region and southwestern Kansas.
 During the overnight hours, the focus for organized heavier
amounts is expected to shift farther to the south.  As a
developing low level center moves across West Texas, models have
remained overall consistent in showing heavier rates developing
along a low level boundary setting up across the South Plains,
northern Permian Basin, the northern Concho valley and the Big
Country.  With thermal profiles suggesting snowfall from the onset
across most areas, sustained lift interacting with ample moisture
is expected to support several hours of moderate to locally heavy
snowfall across the region Sunday morning.  Several current and
time-lagged members of the HREF indicate areas of snowfall rates
in excess of 0.5 in/hr moving east across the region Sunday
morning.  WPC PWPF probabilities indicate that snowfall
accumulations of 4-inches or more are likely across this region. 
Low level forcing is expected to support areas of snow moving east
across portions of central to eastern Texas during the day on
Sunday, before reaching into the ArkLaTex region by late in the
day.  Marginal boundary layer temperature are expected to limit
accumulations on the ground, however areas where heavier rates do
occur will likely be sufficient for at least an inch or two of
accumulating snow.  Greatest potential for significant
accumulations is expected across portions of Central Texas and
western North Texas.  By late Sunday and continuing into the
overnight, there remains a good signal for significant snowfall
developing near the southern ArkLaTex region into northern
Louisiana.  Favorable upper jet forcing along with low level
frontogenesis is expected to support a period of moderate to heavy
snow, with at least an inch or two likely extending from the
ArkLaTex to as far east as central Mississippi.    

For Days 1-3, the probability of significant icing (0.25-inch or
more) is less than 10 percent.

Pereira