Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Sat Jan 12 2019

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


...Central Plains to the Mid-Atlantic...
A major winter storm across portions of the central Plains, mid
Mississippi and Ohio valleys this morning will spread east across
the Mid-Atlantic today as a zonal southern stream jet develops
across the southern CONUS. The main snow feature is the low level
warm front east of the low with the cold conveyor and north and
west of the low in the TROWAL. This west to east swath is
highlighted in Day 1 WPC probabilities with a moderate risk for an
additional 6 inches from just north of St. Louis across central
IL/IN and into southwestern OH. Moderate probabilities for 6
inches are also present on the higher ridges of the central
Appalachians and Blue Ridge where easterly low level flow
encounters upslope forcing.

As the system moves east across the Ohio valley tonight, 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 well into adjacent Piedmont. Day
1 WPC probabilities for a quarter inch of ice are moderately high
from western NC into southwestern VA roughly between I-81 and
I-40. There are moderate probabilities for a half inch of ice in
northwestern NC in the Blue Ridge Plateau.

A coastal low will begin to develop along the Carolina 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 farther to the north. A continued
trend toward higher snow along the low level warm front over the
central Mid-Atlantic is supported by low Day 1 WPC probabilities
for 8 inches that bleed east from the Blue Ridge over central VA.


...California...
Low pressure lingers off the northern CA coast Monday into
Tuesday. A shortwave lobe swings around the low and into central
and southern CA Monday night. Enhanced Pacific moisture and
upslope forcing gives an inch QPF with moderate Day 3 WPC
probabilities for 12 inches in the high Sierra and moderate
probabilities for 6 inches across the rest of the Sierra Nevada.

Jackson