Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 PM EDT Wed Oct 23 2019

Valid 00Z Thu Oct 24 2019 - 00Z Sun Oct 27 2019

...Central Rockies and Southern Plains...
Days 1-2...

A mid-level trough digging through the Rockies Thursday will begin
to close off as it moves towards the Panhandle of Texas. There
remains considerable spread in the guidance into how this system
will evolve Friday into Saturday with respect to the depth of the
low and its progression eastward. The UKMET remains in the middle
of the envelope and relatively consistent with its past few runs,
while the remaining guidance is slowly converging towards it. For
this reason the general blend consisted of the EC/GFS mean with
some targeted adjustments in the Texas Panhandle to include the
high res NAM and CMCreg.

As the trough digs southward, a surface cold front will also push
south into the Southern Plains, producing upslope flow into the
Rockies of CO, and Sangre De Cristos/Sacramentos of New Mexico by
Friday. This upslope flow will force ascent, which will be
enhanced by jet-level diffluence in the entrance region to a 130kt
jet streak. Snow levels may drop as low as 4000 ft in eastern CO
and parts of NM, so the heaviest snow will be confined to the
higher terrain. WPC probabilities indicate a high risk for 8
inches in the high terrain of the Sangre De Cristos and CO Rockies
on D1, with high probabilities for 4 inches extending eastward
into the High Plains including the Raton Ridge.

Further southeast late on D1 and into D2, a stripe of heavy snow
may develop across the TX Panhandle. Guidance has come into better
agreement with this development, and snow probabilities have
increased for Thursday evening/night. A stripe of heavy snow
collocated with a subtly coupled jet structure as the upper trough
sharpens will spread SW to NE in response to a brief but intense
period of 700-600mb fgen within the saturating DGZ. This is likely
to be a situation where rain changes to snow, but heavy snow rates
are possible as noted by negative theta-e lapse rates, which
should overcome marginal temperatures and wet ground. The band is
likely to be narrow, but WPC probabilities have increased to show
a slight risk for 4 inches along portions of the Caprock
Escarpment in the vicinity of Amarillo, with lesser amounts likely
in the lower elevations.


...Northern Rockies...
Day 3...

A cold front will drop southward from Canada Friday night into
Saturday, pushing to the WY/MT border by the end of D3 /Saturday/.
At the same time, an upper trough will dig into the Northern
Rockies, with associated height falls and modest jet diffluence to
aid in ascent already provided by upslope into the Rocky Mountain
Front. Snow levels behind the cold front will drop to 2000-3000
ft, so even elevated valleys and portions of the High Plains
should see accumulating snow. However, the heaviest accumulations
will likely be confined to the highest terrain of the Northern
Rockies and Absarokas where WPC probabilities are moderate for 8
inches.


The probability of significant icing is less than 10 percent.

Weiss