Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 PM EST Thu Dec 26 2019

Valid 00Z Fri Dec 27 2019 - 00Z Mon Dec 30 2019

...Southwest U.S....
Days 1-2...

A closed low moving southeast off the southern CA coast this
afternoon today will swing east over the northern Sea of Cortez
tonight before opening and ejecting northeast across the
south-central Rockies through Friday night. Precip and mountain
snow will taper off over the southern CA this evening as the
system shifts east. Probabilities for an additional for or more
inches over the San Bernadinos is moderate to high.

Precip over AZ tonight will be at lower rates as less moisture
makes it inland to the Desert SW. However, the southwest flow
ahead of the upper trough places windward locations is sustained
upslope flow late tonight thru Friday. Day 1 WPC probabilities for
8 or more inches is moderate for the highest terrain in AZ along
the Mogollon Rim to the White Mtns, the highest terrain of
northern NM, and the San Juans/Sangre de Christos of southern CO.
High probabilities for 12 inches or more are over the San Juans
for Day 1.5.


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

Lee side surface low pressure develops over eastern NM late Friday
and moves northeast across western KS Saturday before pushing into
southern MN (per the WPC preferred track) Sunday.
Confidence in the track of the surface low has increased with the
12Z deterministic suite with some uncertainty still with the depth
of the mid-level low and axis of comma head precip over the
northern Plains. A preferred blend of the 00Z ECMWF/ECENS/UKMET
with very limited inclusion of the GFS/NAM went into the QPF. This
results in low to moderate confidence for 6 or more inches on Day
2 from northeast CO across western/central NE into SD, blossoming
to moderately high probabilities for 6 inches or more across the
eastern Dakotas and northern MN on Day 3. Probabilities for 12
inches or more are around 20 percent in the core of this swath on
Day 3.

A precip type transition zone will occur along and just west of
the the low track, resulting in freezing rain accumulations given
the cooling and drying antecedent conditions as high pressure
builds across the area Friday. Low to moderate Day 2 probabilities
for a quarter inch of ice from central NE to southern MN by way of
far southeast SD/northwest IA, then across to northern WI.  

...Northeast...
Day 1...

A warm front lifts across northern NY and northern New England
tonight into Friday. Surface temperatures area below freezing
ahead of this front with warm low level air on the back side of
high pressure providing a warm nose. WPC Day 1 probabilities for a
quarter inch of ice are generally around 20 percent for northern
VT/NH into north-central ME.

Jackson