Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EST Tue Dec 12 2023

Valid 12Z Tue Dec 12 2023 - 12Z Fri Dec 15 2023


...Michigan U.P. into the Tug Hill...
Days 1-2...

Lake effect snow appears likely behind a cold front over portions
of the Great Lakes and Northeast Tuesday night into Wednesday. WPC
snow probabilities for 4"+ remain moderate to high (60% to 90%) in
eastern sections of the U.P. shoreline of Superior. Also of note
is the likelihood for a resurgence in lake effect single-band snow
east of Ontario into the Tug Hill during the day Wednesday, with
WPC probabilities for 4"+ moderate to high (40-70%).


...Southern Rockies into the High Plains...
Days 2-3...

A shortwave trough diving southeast across OR/CA/NV this morning
gets ducted under an amplifying northern stream ridge over western
Canada today and will intensify into a closed low over the
Southwest by tonight. As this closed low slowly moves eastward an
impressive amount of moisture will be advected northward out ahead
of it. PW values are expected to approach mid December records
over portions of northeast NM into southeast CO into the High
Plains. This ample moisture combined with the strong mid/upper
forcing associated with the closed low and areas of orographic
enhancement will result in a significant snow event for portions
of the area Wednesday into Thursday. The heaviest snowfall is
expected across the favored terrain of the Sangre de Cristos,
where upwards of one to two feet is expected. Across the rest of
northeast NM north and east of the Sangre de Cristos, the
probability of exceeding 8" of snow is over 60%, with these higher
probabilities spilling into adjacent areas of far southeast CO as
well. Overall there is high confidence in a significant snowfall
across these areas of northeast NM, with impressive ECMWF EFI
values noted as well.

Confidence in snowfall amounts and impacts decrease as you head
eastward into the TX/OK Panhandle and southwest KS. There are some
more notable thermal differences amongst the models here, which
makes nailing down the snow forecast tricky. Overall it will be a
pretty marginal thermal environment over these further east areas,
and we will likely need some dynamic cooling to get temperatures
cold enough for accumulating snow. Given the impressive dynamics
with this system, we did lean a bit more towards the colder
solutions...but even in these model solutions a transition to
heavy snow is not clear cut. Nonetheless, leaning against the
warmer GFS/GEFS and more towards the CMC/ECMWF/ECENS/NAM does
result in some accumulating snowfall from western KS into the TX
Panhandle Wednesday night into Thursday. Any notable probabilities
of 4"+ amounts are confined to the northwest TX Panhandle into the
far western OK Panhandle and far southwest KS...where
probabilities are generally 30-50%. It should be noted that there
are some low end probabilities of 6-8"+ amounts, and a more
dynamic system and quicker changeover to snow would result in
these higher amounts being realized. At the moment this is a lower
probability event, but certainly something worth monitoring. Given
the impressive moisture and forcing associated with system, there
is certainly higher end potential...but at the moment the marginal
thermal profiles suggests the most likely outcome is more in the
~1-4" range.

While some light freezing rain is possible (30-60% chance of
exceeding .01") across portions of northwest KS and southwest NE
on Wednesday, the probability of significant ice (greater than
0.10") is less than 10% across the CONUS.    

Chenard