Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 PM EST Sun Jan 23 2022

Valid 00Z Mon Jan 24 2022 - 00Z Thu Jan 27 2022

...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

Expansive cyclonic flow over much of Canada into the northeastern
1/3 of the CONUS will persist through the next 3 days and periodic
embedded shortwaves moving through the fast flow on its south side
will support episodes of light to occasionally moderate snow. One
clipper, currently over the central Appalachians, will bring
mostly light accumulations to portions of the Mid-Atlantic and
Northeast through tonight before the wave moves offshore. Another
shortwave trough is pushing into the northern Plains this
afternoon and is expected to take on a track through the Upper
Midwest to lower Great Lakes through tonight through tomorrow
night. While this wave lacks the stronger/deeper forcing compared
to the one from yesterday to early this morning, it does have a
similar track. With upwards of 0.20" expected in QPF and SLRs
hovering around 20:1 or so, a stripe of 2" to locally 4" is
expected with this system as it pushes through portions of the
Upper Midwest into northern IN, northern OH, and southern MI. Some
enhanced totals will be possible off the southern/southeastern tip
of Lake Michigan and off Lake Erie where enhanced LES bands are
possible. The greatest signal for 4 inches or more in the latest
WPC probabilities are off southern Lake Michigan for northwest IN
and southwest MI where the signal is above 90 percent while
moderate probabilities are found off Lake Ontario favored snow
belt region. After that clipper shortwave, a relative lull in
precipitation is expected with only localized LES bands expected
late on day 2 into day 3 as the flow becomes less conducive for
significant snow bands.


...Rockies...
Days 2-3...

Compact mid-level shortwave rough dropping through the west side
of the Rockies early next week will bring a broad area of upper
diffluence over the next few days. A lack of moisture initially
will confine snowfall accumulations to mainly under 4 inches
across Montana for day 1 but by day 2/3, the combination of the
upper diffluence and upslope flow from high pressure slipping down
through the Plains will help focus stronger lift over the terrain
and foothills of the CO Front Range and even into the lower
elevations of Rocky Mountain Piedmont. The 12Z guidance trended a
bit wetter across the board now showing potential for QPF to
exceed 0.25" on day 2 for DEN and with SLRs in the 10-15:1 range,
several inches of snowfall will be possible as this system drops
south. By day 3, the snowfall threat will reach eastern NM and the
TX Panhandle where some uncertainties in moisture/lift
availability will keep accumulations mainly light at this point.

The latest WPC probabilities for 4 inches are greatest on day 1
across south-central Montana then reach moderate to high levels on
day 2 for the Front Range into the DEN metro. By day 3 those 4
inch probabilities drop to under 20 percent across NM and TX
Panhandle.



For days 1-3, the probability of significant icing is less than 10
percent.


Taylor