166
FOUS11 KWBC 080737
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
237 AM EST Fri Nov 8 2024

Valid 12Z Fri Nov 08 2024 - 12Z Mon Nov 11 2024


...Central/Southern Rockies and Adjacent High Plains...
Days 1-2...

...Heavy snow and major impacts continue for the Southern
Rockies and Interstate 25 corridor into Saturday morning...

Significant winter storm will persist across eastern CO through
very early Saturday morning before ending. The primary driver of
this impressive system is an anomalous upper low which will be
moving across New Mexico this morning before slowly ejecting to the
northeast and into the Central Plains on Saturday. NAEFS height
anomalies reach as low as -3 sigma, indicating the strength of this
feature, and the resultant downstream height falls and divergence
will combine with a modestly coupled jet structure to produce
impressive large-scale ascent across the Southern/Central Rockies
and High Plains.

This evolution today will also drive surface low development over
Texas, and this wave will lift northward into Saturday. This low
will be accompanied by enhanced forcing through persistent moist
isentropic lift, especially along the 295K surface where mixing
ratios climb to 4-6 g/kg, lifting into a robust TROWAL pivoting
over the region Friday aftn/eve. Additionally, an axis of elevated
instability is likely beneath the TROWAL and collocated with an
axis of deformation, which suggests intense snowfall rates within a
pivoting band of snowfall. Omega maxima into the DGZ, although
subjectively elevated, will support heavy snow rates which the WPC
snowband tool indicates will reach 1-2"/hr. It is possible that
some rates may briefly even reach 2-3"/hr as model cross-sections
indicate a narrow corridor of theta-es lapse rates <0C/km
collocated with EPV<0 suggesting the potential for upright
convection. Regardless, a highly impactful snow is expected again
Friday from far northeast NM into much of eastern CO.

The heaviest accumulations are likely in the higher elevations of
the Raton Mesa, Palmer Divide, and into the Sangre de
Cristos/southern Front Range, but intense ascent should allow for
snow significant snow accumulations even into the High Plains, at
least until the more intense easterly/WAA develops warming the
column. There will likely be a thermal gradient near the KS/CO
border which will be the demarcation between primarily snow and
primarily rain, but even all the way to the KS border periods of
snow are possible during heavier snow and dynamic cooling.
WPC probabilities for more than 8 inches of additional snow on D1
are above 80% across the Raton Mesa and Palmer Divide, as well as
into the Sangre de Cristos and southern Front Range. Elsewhere,
probabilities for more than 4 inches are high across much of
eastern CO except towards the KS border and northeast corner.

As the low occludes and shifts over Neb Friday night/Saturday, the
moisture moisture fetch is shunted east and thermals farther east
do not support snow, so the heavy snow threat generally ends in CO.
Some lingering snowfall is likely, however, especially in the CO
Rockies, but additional accumulations will likely be minimal.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss


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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

$$