Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
453 PM EDT Mon Oct 26 2020

Valid 00Z Tue Oct 27 2020 - 00Z Fri Oct 30 2020


...Southern Rockies/Plains...
Days 1-3...

A positively tilted upper trough over the Desert SW this afternoon
closes into an upper low over the southern AZ border tonight
before drifting east-northeast across NM through Tuesday night
before crossing the southern Plains through Wednesday night. Heavy
snows will settle across NM, esp above about 4000ft, tonight
before shifting east to the southern High Plains into Wednesday
night under the closed low. Meanwhile, another round of
significant ice accretions are expected over western/central OK
and northwest TX into southeast KS late tonight into Tuesday
before the ice risk shifts west toward the TX Panhandle Tuesday
night as comma head precip (and a tight precip type transition
zone) increases as a dry slot develops farther west. Thermals from
the 12Z ECMWF are preferred for Days 2/3 (00Z Wed to 00Z Fri)
which depicts a much more defined comma head/dry slot to the east
(and in decent agreement with the 12Z CMC/UKMET) than the 12Z GFS
which is less occluded.

Strong lift and ample Pacific moisture interact with very cold air
spilling south into the developing low and continue to support
heavy snows over mainly central NM ranges tonight. Day 1 snow
probs are moderate to high for 6 or more inches for the Sandia
Manzano, Sacramento, and San Mateo mountains among others in
central NM.

Following a period of scattered, light precipitation this evening,
organized heavier and mixed precipitation is expected to return
portions of the southern Plains late tonight into Tuesday. As the
upper low begins to turn east, increasing lift and a surge of
deeper moisture will raise the potential for higher precipitation
rates across portions of western and central Texas into Oklahoma,
with another round of significant ice accumulations possible from
the Texas Hill Country northward into central Oklahoma.  The
heaviest storm total ice accumulations are expected to center
across southwest into central Oklahoma, where WPC PWPF shows
moderately-high probabilities for ice accumulations exceeding a
quarter-inch.  Meanwhile within the deeper cold air of the comma
head, periods of heavier snow are expected across the western
Texas Panhandle and eastern New Mexico where Day 1.5 snow probs
are moderate to high for 4 or more inches.

As the upper low moves east of the southern Rockies on Wednesday,
southerly winds ahead of a developing low level circulation will
end the potential for additional snow/ice accumulations across
central Texas and Oklahoma. However, cold air on the backside of
the system should be sufficient for additional accumulating snow
and some ice accumulations continuing through early Wednesday
across the Panhandle region and northeastern New Mexico, before
lifting farther north into eastern Colorado and western Kansas
late in the period as noted by Day 2 snow probs for 4 or more
inches along the NM/CO border to the western TX Panhandle, and
moderately high Day 2 ice probabilities for a tenth inch or more
over western OK and the northeastern TX Panhandle into southwest
KS.

Jackson