FOUS11 KWBC 020840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Thu Jan 2 2025

Valid 12Z Thu Jan 02 2025 - 12Z Sun Jan 05 2025

 ... Part 2/2 ...


...Northern High Plains... Day 3...

A stripe of heavy snowfall is becoming more likely Saturday from
central MT through western SD. This snowfall will be associated
with a slowly advancing warm front topped by increasing divergence
downstream of a potent shortwave digging into the Four Corners
region. While jet dynamics are weak during this time, the
downstream moist advection on impressive 280-290K isentropic ascent
should expand precipitation in a NW to SE fashion late Friday night
and through Saturday. Robust 850-700mb fgen into this moistening
column will help intensify ascent resulting in heavier snow rates,
but at this time the intensity of this snow is still uncertain due
to modest DGZ depth probabilities and a lack of ideal overlap
between the best ascent and the DGZ. Still, a band of moderate to
heavy snow is becoming more likely. WPC probabilities have 
increased to 50-80% for 4+ inches across north-central MT, with
40-50% chances for at least 6 inches by Saturday night.


...Central Plains through the Mid-Atlantic...

A significant winter storm is becoming more likely late Saturday 
through Monday, with the onset of light freezing or frozen 
precipitation beginning Saturday evening across Kansas. At this, 
time, WPC probabilities for significant snow are minimal through 
the end of D3 (Sun morning), but heavy snow is expected to be
developing at that point and continuing to into D4 and beyond. The
upper low swinging through the Great Basin on Saturday is expected
to eject into the central Plains Saturday night while closing off
and strengthening within a developing favorable duel jet structure.
Strong WAA will develop and blossom the precipitation shield across
the central Plains and Mid-Mississippi Valley Saturday night while
also promoting a warm nose to lift northward. This creates a
favorable setup for mixed ptypes and wide swath of sleet/freezing 
rain. Guidance has trended slightly north with QPF and the mix zone
in recent runs as is common for WAA regimes with a surface High 
remaining displaced to the NW. It's possible the warm nose trends 
farther north as hires CAMs become available, also impacting areas
downstream by D4. WPC ice probabilities have increased by the end 
of D3 and are 20-40% for at least 0.1" of freezing rain accretion 
from central KS to southern Missouri. For this system, WPC has 
initiated Key Messages which are linked below, and more information
can be found in the WPC extended range discussion as well.

Snell/Weiss

...Winter Storm Key Messages are in effect. Please see current 
 Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/La...

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