Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Sun Feb 02 2020

Valid 12Z Sun Feb 02 2020 - 12Z Wed Feb 05 2020

...Pacific Northwest through the Southern Plains...
Days 1-3...

An amplifying but remaining positively tilted trough will dig
across the Mountain West through early in the week. This feature
will be accompanied by increasing Pacific moisture into the
Rockies. Ascent will become increasingly robust through RRQ
jet-level diffluence combined with PVA and height falls, to drive
an extended period of heavy snowfall in the Rockies. Additionally,
beneath this synoptic lift, a surface low is expected to track
ahead of the slow moving trough/low both over the Mountain West
(NV and UT) Sunday/Sunday night with further lee side development
in the central High Plains. This low pressure, along with surface
high pressure shifting south over the northern Canadian Prairies
will drive moist easterly upslope flow into the mountains of
CO/WY, further enhancing precip Sunday night through Monday night.
Significant snowfall is expected.

Snow levels this morning will fall quickly as the cold front
shifts southeast and the upper trough digs through the CONUS. This
will drive snow levels down to below 500ft across most of the West
north of New Mexico by Tuesday, and towards the Mexican border
Wednesday. These lowering snow levels combined with the prolonged
and significant forcing will produce 2 days of heavy snow across
WY where WPC probabilities are high for 18 inches in the terrain,
especially the Wind Rivers and Big Horns, and 2 day totals could
reach 3 feet in places. Elsewhere, WPC probabilities are high for
6 inches across eastern ID, southern MT, and the high terrain of
the northern Great Basin on Day 1, shifting southeast into CO and
the High Plains of SD/NE on Day 2.

The upper trough will begin to shear to the east Tuesday morning
driving the best moisture convergence and ascent into the Southern
Plains invof the Panhandle of Texas. As mid-level flow remains
SWly and surface high pressure extends across the Plains, robust
isentropic lift will overspread the region. This ascent combined
with intensifying fgen and a secondary jet streak lifting into the
Central Plains will place parts of NM/TX/OK in a region favorable
for heavy snowfall. The guidance depicts two camps, the Non-NCEP
solutions are a bit warmer and further north than the NCEP camp,
but are preferred, and this suggests a stripe of moderate to heavy
snow is likely on Tuesday. WPC probabilities for 4 inches are
moderate in the Texas Panhandle, but high in the terrain of New
Mexico including the Sacramentos and Sangre De Cristos.

As this leading storm sinks into Texas, another round of heavy
precipitation will move into Washington. WPC probabilities are
high for 6 inches in the Olympics and Cascades of Washington
Tuesday into Wednesday.


...Northeast...
Day 1...

An impulse in a strong northwesterly jet pushing from the Great
Lakes Sunday to New England Sunday night will bring some snow to
these regions. A swath of light snow is likely across upstate NY
Sunday within the modest forcing associated with this feature.
Lake effect snow off Lakes Erie and Ontario allows WPC
probabilities for 4 inches be moderate for the Tug Hill today with
lower probabilities for western NY just east of Lake Erie.


The probability of significant icing (0.25-inch or greater) is
less than 10 percent.

Weiss