Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 AM EST Thu Nov 28 2019

Valid 12Z Thu Nov 28 2019 - 12Z Sun Dec 01 2019

...Western U.S...
Days 1-3...

Broad but intense upper low will continue to plague the west,
while spokes of energy rotate cyclonically around it. The primary
upper low will drift into the Great Basin into Friday, before
splitting, with the primary energy moving into the Northern Plains
while subsequent re-deepening occurs in response to new energy
dropping out of the Pacific off the Oregon coast. While the former
will eventually lead to strong cyclogenesis in the Plains, the
primary low and the wave re-deepening off the Pacific Coast will
continue to spread moisture into the Mountain West. Deep SW flow
on the southern edge of these upper features will advect
significant moisture across the West, with height falls, PVA, and
jet level diffluence all working together to produce deep layer
ascent. Orographic enhancement to the flow will result in heavy
snowfall...with snow levels falling below 1000 ft to the north,
and as low as 3500 ft in AZ/NM.  By late Friday night and
Saturday, most of the energy will lift into the Plains bringing a
respite from the snow except in the northern Wasatch and points
northeast.

...Maine...
Day 1...

An upper low across the Great Lakes will continue to move quickly
eastward early this morning.  Snowfall should linger over parts of
Maine into mid-morning with additional accumulations being
light...although ensembles show that there is a small probability
of snowfall amounts exceeding 4 inches before the snow ends.

...New Mexico/Texas...
Day 1...

On-going wintry combination of snow...sleet and freezing rain will
linger over portions of eastern New Mexico and western Texas into
the late morning or early afternoon.  Some snowfall amounts in
excess of 8 inches are possible in some of the mountains through
the afternoon, while places at lower elevations of southeast New
Mexico and adjacent parts of West Texas should gradually be
transitioning to rain.  Some light snow accumulations are likely
in the High Plains and Texas Panhandle, with much higher amounts
likely in the terrain of New Mexico including the Sangre De
Cristos.

...Central/Northern Plains...
Day 3...

...Significant Winter Storm possible beginning Friday night...

A closed low across the Great Basin will fill as it ejects
northeast, but will re-energize and deepen into a negatively
tilted closed low over the western High Plains. This combined with
an increasing jet streak to the south will drive cyclogenesis in
the lee of the Rockies which will then rapidly deepen as it lifts
northeast into the Northern Plains. While there remains
considerable spread in the guidance, the 27/18Z and 28/00Z runs of
the GFS were considerably deeper with the surface cyclone and was
considerably warmer than other guidance.  As a result, little
weight was given to the GFS for QPF or thermal fields in this
forecast cycle.  As mentioned in the previous discussion, there is
some possibility that the mid-level low and surface low stalls in
response to blossoming ridging to the north, so a prolonged snow
event seems likely from the Dakotas into Minnesota and parts of
the Great Lakes.

Bann