Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EST Fri Jan 11 2019

Valid 00Z Sat Jan 12 2019 - 00Z Tue Jan 15 2019


...Central Plains to the Mid-Atlantic...

A major winter storm will continue to unfold Friday night into
Saturday across portions of the central Plains, mid Mississippi
and lower Ohio valleys.  Models continue to signal moderate to
heavy snows from western Kansas to the lower Ohio valley that will
be associated with a well-defined southern stream shortwave moving
east of the Rockies.  Heaviest amounts are expected to center from
central Missouri eastward into central Illinois.  A prolonged
period of warm air advection into an area of low-mid level
frontogenesis and divergent flow aloft is expected to support
heavier precipitation rates across this region.  This is expected
to provide some compensation for lower snow to liquid ratios
afforded by lift outside of the dendritic growth zone and warmer
air mixing aloft.  This period of warm advection precipitation
followed by the trailing deformation zone is helping to the
support the high WPC Day 1 probability for accumulations of
8-inches or more.  WPC Day 1 probabilities also indicate an
embedded Moderate Risk for accumulations of a foot or more within
this area.

As the upper system begins to shear east, models continue to
indicate lighter amounts extending east along the Ohio valley into
central Appalachians on Saturday.  As the shortwave moves east
across the Ohio valley Sunday morning, moisture will spread across
a strong wedge of shallow cold air, setting the stage for freezing
rain and significant icing for portions of the southern and
central Appalachians into adjacent Piedmont.  A coastal low will
begin to develop along the southern Mid Atlantic coast Sunday
morning.  With deeper cold air in place, warm advection spreading
east of the mountains followed by additional precipitation west of
the developing low may contribute to some significant snow/sleet
amounts further to the north.  The overall trend was toward a more
northerly low supporting higher probabilities for amounts of
4-inches or more further to the north.

Pereira