Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 AM EST Thu Dec 14 2023

Valid 12Z Thu Dec 14 2023 - 12Z Sun Dec 17 2023


...Southern Rockies into the High Plains...
Days 1-2...

Current analysis early this morning shows an anomalously deep
closed upper level low centered over east-central Arizona,
drifting eastward through the Four Corners region. Downstream of
this feature, very impressive upper divergence combined with a
fairly strong surface high over the Eastern U.S. is helping to
funnel plenty of low level Gulf moisture into the region. The
large scale forcing and impressive moisture is resulting in
widespread precipitation across portions of the southern Rockies
and High Plains. Thermally, profiles are marginally supportive for
heavy snow outside of terrain areas at least initially, but with
the approach of the closed upper level, some cooling in the column
combined with dynamical effects, intense snow rates resulting in
heavy snowfall accumulations are expected, particularly for
portions of northern New Mexico followed by portions of OK/TX
Panhandles and southwestern KS later today/this evening. The
latest WPC snow band probability tracker prototype shows high
probability of 1-2"/hr rates in the San Juans and Sangre de
Cristos, likely due to the stronger upslope flow contributions.
But even further east, the snow band tracker is suggesting a
narrow/localized area of higher snowfall rates up to 1-1.5"/hr
between 18Z-06Z from southeast CO through the OX/TX Panhandles and
southwest KS.

For the Day 1 period (12Z Thursday-12Z Friday), the latest WPC
snow probabilities show the greatest probabilities for at least 4
inches to be mainly in the terrain areas (San Juans and Sangre de
Cristos) where probabilities exceed 80%. Probabilities of at least
8 inches reach 40-50 percent. Further east away from the terrain,
the probabilities of at least 2 inches is up to 50 percent though
several members in the latest WSE show higher totals between 3-4".

For Day 2 (12Z Fri-12Z Sat), a secondary area of heavy snow
appears increasingly likely Friday morning/early afternoon
underneath of the core of the upper level as it drifts eastward
through Kansas. This is a bit more low confidence given the
marginal thermal profiles and questionable lift/forcing that is
expected to be on the downward trend beyond 12Z Friday but
something to monitor if trends continue for a colder, wetter
scenario.


...Northern Plains and Upper Midwest...
Days 2-3...

A shortwave trough moving south/southeast from Saskatchewan into
the Northern Plains Friday will work with a 250 mb jet streak to
provide modest large scale forcing for ascent over the Northern
Plains to Upper Midwest Friday through early Saturday morning.
Meanwhile, a weak area of low pressure is set to form over the
Midwest before sliding southeast with the developing mid/upper
level closed low. Low level moist flow overrunning a warm front
draped in the vicinity will result in a west to east oriented band
of precipitation to break out from the eastern Dakotas through
northern Minnesota. Thermally, forecast soundings show a fairly
marginal/challenging setup for significant accumulating snow.
However, the trend in the 00Z guidance and the latest WSE plumes
suggest some outlier heavier bands may develop most likely due to
strong dynamic cooling helping to offset the marginal thermals,
resulting in localized heavier wet snow bands. The latest cycle of
the WPC snow probabilities show upwards of 20-30 percent of at
least 2 inches, generally over the Arrowhead of Minnesota where
moist easterly flow off Lake Superior and terrain enhancement will
work to provide an boost to snowfall potential. The setup
certainly bears watching for additional strengthening/higher
snowfall potential over the next few forecast cycles.


Taylor