Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 AM EST Tue Nov 19 2019

Valid 12Z Tue Nov 19 2019 - 12Z Fri Nov 22 2019

...Northeast...
Day 1...
A low of southern stream origins continues to lift north from Nova
Scotia this morning with associated wrap around precipitation
changing over to mainly snow as a trailing mid-level northern
stream trough low lifts northeast from eastern PA, passing Maine
by this evening. The main northern stream trough moves through
Tuesday night into Wednesday, but the surface low is expected to
be farther east than this current one with little associated
precipitation over the Northeast. Day 1 snow probabilities for
four inches are limited to far northern Maine and freezing rain
potential after 12Z is expected to be under a tenth inch centered
on the White Mtns of NH.


...Southwest from California across the Central Rockies...
Days 1-3...
Prolonged precipitation event from multiple upper lows will occur
across the region through Thursday.

Low pressure crosses northeast over the northern Baja Peninsula
tonight and eject across the Four Corners region through
Wednesday. Meanwhile, a more potent upper low will develop over
northern California this evening and merely drift east over the
southern Great Basin through Thursday before shifting east across
the across the south-central Great Plains. As the initial low
fills and lifts northeast toward AZ today, snow-levels will be
above 10,000ft in this tropically sourced air mass. However,
height falls under the remnant trough allow the 700mb temp (near
10,000ft) to drop below 0C and allow snow to begin tonight on the
highest terrain (above 9000ft) in AZ, southern UT, and southern CO
in the widespread heavy precipitation. The Day 1.5 risk for 8
inches or more is moderate to high in the San Juans and southern
Wasatch. Snow levels drop to around 6000ft under the second low
tonight across southern and central CA where Day 1.5 probabilities
for 4 inches are moderate to high across the other Sierra Nevada,
the Spring Mtns west of Las Vegas and the highest San Bernadino
Mtns.

The California closed low will push into the southern Great Basin
Wednesday night, keeping the tropical Pacific moisture feed into
the Four Corners region. Snow levels continue to fall to around
6000ft just ahead of the low with heavy snow expected for the
higher terrain in these states. Widespread moderate to high
probabilities exist for 8 inches above 6000 ft from the Mogollon
Rim across the Wasatch to the Unitas, the San Juans, Sangre De
Cristos. More moderate 8 inches probabilities extend across the
Great Basin ranges, and ranges and even high plains of southern
Wyoming.


...Northern Rockies to Lake Superior...
Days 1-3...
Northern stream energy crosses the northern Rockies from WA today
with an axis of precip near the the northern MT/ND border where
there are moderate probabilities for four inches extending along
the border. The main northern stream trough then sweeps across
this area Wednesday, pushing mainly light snow across the Dakotas
until remnant energy from the low ejecting from Baja California
today lifts northeast across the north-central Plains Wednesday
night with rapid cyclogenesis on a surface low track from KS to
the Mackinac Strait. This reinvigorates the precipitation with
moderately high probabilities for four inches over northern MN in
Day 2.5.


Jackson