Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 PM EST Sat Jan 21 2023

Valid 00Z Sun Jan 22 2023 - 00Z Wed Jan 25 2023

...Rockies and High Plains...
Days 2-3...

Shortwave energy moving onshore the Pacific Northwest today quick
digs through the Great Basin to the Desert Southwest by Sunday
evening. Favorable left exit jet dynamics over the terrain will
favor some locally heavy snowfall from portions of the northern to
central Rockies but the relatively fast progression and limited
moisture suppresses any significant snowfall total. The mid/upper
level feature is then expected to close off near the Four Corners
region Sunday night into Monday. The trend in the 12Z guidance has
been for a more suppressed/southwest shift in this feature,
resulting in less QPF for the central Rockies and an overall
slower timing. By Monday night into Tuesday, the upper low gets
picked up and ejects out into the southern Plains where favorable
jet dynamics leads to surface low developing over western TX. With
a favorable source of Gulf moisture wrapping around this system,
localized banding of heavy snow is possible across portions of
eastern NM into the TX Panhandle and perhaps into parts of OK late
Tuesday. However, model guidance continues to struggle with the
evolution of the upper closed low and further slowing/southward
trends could continue. However, the set up does favor some heavy
snow and right now based on the WPC PWPF, the greatest
probabilities of seeing 4" or greater of snow are from Sacramento
and Sandia-Manzano Mtns and then across portions of the TX
Panhandle with upwards of 40-50% probabilities. The latest PWSSI
for Moderate impacts shows a broad area of 40-60% probabilities
suggesting potential for hazardous travel conditions and
disruptions though confidence isn't too high with this setup and
further changes in the track and potential heavy snow are likely.

...Northeast...
Days 1-2...

Split flow across the central U.S. today featuring a compact
shortwave trough over the Plains and northern stream energy
passing through the Upper Midwest will phase and deepen through
tomorrow morning. The positively tilted trough begins to take on a
neutral tilt while at the surface, low pressure organizing along
the Gulf Coast will rapidly lift northward toward the northeast.
Strong WAA at low-mid levels out ahead of the trough and a rich
reservoir of moisture will stream from the Gulf Coast up the East
Coast Sunday afternoon. PWs by 00-06Z Monday range between
0.5-0.75" from southern PA up the East Coast and into portions of
southern New England, which is right around the 90th
climatological percentile according to NAEFS. High pressure over
the Northeast Sunday morning will be retreating east into the
northwest Atlantic, leaving the lingering area of sub-freezing
temperatures without much of an anchor to keep any of the already
marginally cold temperatures in place.

Not a lot of significant changes with the 12Z guidance and the
latest WPC PWPF shows the greatest probabilities of greater than
6" o snow from the southern Adirondacks northeast across southern
VT and much of NH and southern to central ME with a stripe of 50
to 70% probabilities. Given the marginal thermal environment, the
greatest totals will be elevation dependent and the higher terrain
areas of southern VT through ME could see localized totals of
8-10". This also lines up well with the area of the best banding
potential just northwest of the low track late Sunday into Monday
morning. Not a lot of change in the PWSSI showing a broad area of
40% or greater suggesting hazardous travel and disruptions to
daily life may occur.

...Pacific Northwest to the Northern Rockies...
Days 1-3...

An potent but fast-moving disturbance just off the coast of
British Columbia this morning is set to bring more mountain snow
into the Olympics and northern Cascades through tonight. Locally
heavy accumulations will be confined to the higher peaks of these
ranges.  Model consensus is in agreement on the trough amplifying
as it moves southeast into the interior Northwest tonight then
across Utah Sunday. Still not anticipating any widespread heavy
amounts, but locally heavy accumulations are possible from
northern Idaho to the western Montana ranges. Northerly winds in
the wake of a low level frontal passage moving east from the
Rockies into the High Plains will provide some upslope enhancement
and cause some higher snowfall totals in the mountainous terrain
of central Montana Sunday afternoon and into Sunday night. 


Mullinax/Taylor