Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 PM EST Wed Dec 25 2019

Valid 00Z Thu Dec 26 2019 - 00Z Sun Dec 29 2019

...Southwest U.S....
Days 1-3...

The closed, primary low in the Western U.S. trough is off the
northern CA coast this afternoon and will shift south to the
northern Sea of Cortez through Thursday night before ejecting
northeast across the south-central Rockies Friday night.
Strengthening onshore flow, along with increasing upper divergence
will support heavy precipitation into the mountains of southern CA
tonight through Thursday. Snow levels will remain around 4000ft
through this event across southern CA, with heavy snow
accumulations expected for the Transverse Ranges, southern Sierra
Nevada and Peninsular Ranges. Total accumulations of 2ft are
expected shortly into the snow elevation zone, with locally
heavier totals expected across the highest elevations.

Heavy precipitation spreads across the southern Four Corners
region Thursday night/Friday with continued heavy snow (snow level
generally around 5000ft in AZ/NM). Low to moderate probabilities
for a foot or more are over the highest peaks in AZ/northern NM,
and the San Juans Sangre de Cristos into CO on Day 2 and 2.5.

...Central and Northern Great Plains...
Days 2,3...

Lee side surface low pressure develops over eastern NM late Friday
in advance of the mid-level low. The exact track of this low
remains uncertain with the GFS farther east than the
ECMWF/UKMET/CMC. The preferred farther western track would have
upslope snow enhancement on the central/northern high plains of
CO/NE/WY/SD on Day 3 with plenty of Gulf moisture available to
wrap into the comma head. Will need to monitor progress of model
solutions on this system. As of now lower Day 3 probabilities for
six inches exist over the western half of NE, far northeastern CO,
southeastern WY, and into SD.
Conceptually a wintry mix transition zone would occur along of the
low track which does appear in low to moderate Day 3 probabilities
for a tenth inch of ice over northeast NE into southern MN,
clipping SD and IA along the way. As of now there are 10 to 20%
probs for a quarter inch of ice near the common border of MN/IA/SD
into northeast NE.


...Northeast...
Days 2...

A warm front lifts into western NY Thursday night with cold
antecedent conditions from a 1030mb surface high expected over New
England Thursday will allow for a wintry mix with freezing rain
the greatest risk to lower elevations. Day 2 probabilities for a
tenth inch are moderately high over northern VT/NH/ME.

Jackson