Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
233 PM EST Tue Jan 25 2022

Valid 00Z Wed Jan 26 2022 - 00Z Sat Jan 29 2022

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

Broad cyclonic flow across the Great Lakes and eastern CONUS will
be reinforced by a cold front Thursday, bringing impressive and
renewed CAA across the Great Lakes. Despite the lack of any
significant synoptic ascent through the period, pronounced NNW
flow within the CAA each day will lead to favorable conditions for
Lake Effect Snow (LES). On D1 /Tuesday night and Wednesday/ the
heaviest snow is likely east of Lake Erie into the Chautauqua
Ridge where pronounced ascent with effective fetch from Lake Huron
will drive heavy snowfall, and WPC probabilities for 4+ inches are
above 50%. Lighter snows are likely along the eastern shore of
Lake Michigan and in the eastern U.P. as well D1.

On D2, brief shortwave ridging blossoms across the Lakes ahead of
the next impulse and cold front progged to cross to the east
Thursday morning. This will likely bring a reduction in forcing
for LES, leading to a rapid wane in coverage and very little LES
is expected. However, late D2 the front approaches and then
crosses from NW to SE. This will rejuvenate the CAA and while
snowfall along the front should be light, enhanced LES is likely
once again, especially D3. The most robust LES D3 is likely south
of Lake Michigan where a single convergent band is likely to
develop with intense omega into a near-surface DGZ. WPC
probabilities are low for 4+ inches at this time, but locally
higher values are possible, and may be reflected better within the
high-res guidance windows during later updates.


...Southern Rockies and High Plains...
Day 1...

A cold front which has pushed up against the Front Range this aftn
will continue to sink slowly southward towards the Mexican border
on Wednesday. As this front drops southward, a robust but slowly
weakening shortwave will pivot out of the Four Corners area and
advect into the Southern Plains. Modest height falls and mid-level
divergence will combine with intensifying RRQ upper diffluence
across TX and NM to produce deep layer ascent in an environment
characterized by PWs of +0.5 standard deviations above the climo
mean. This synoptic lift will be enhanced by both upslope flow
behind the front into the terrain of NM, and mid-level fgen, and
theta-e lapse rates are progged to approach 0C/km. This suggests
intense snowfall rates of at least 1"/hr at times as forecast by
the HREF and WPC snow band prototype tool, and is likely based off
upstream observations across KS/CO this aftn. WPC probabilities
for 6 inches are as high as 50% in the Sangre De Cristos and
northeast High Plains of NM, with locally higher amounts likely.
Lesser amounts but still heavy snow rates are likely into the TX
Panhandle and parts of OK/KS as well. late D1 and into early D2
the shortwave is forecast to weaken substantially and become
absorbed into the westerlies as it sheds towards the MS VLY,
bringing an end to the snowfall Wednesday night.


...Southern Appalachians through the Mid-Atlantic...
Day 3...

Shortwave energy dropping out of the Great Lakes Friday morning
will attempt to phase with southern stream energy moving through
the Southern Plains Friday aftn. While guidance still features
considerable spread in the timing and placement of these features,
confidence is increasing that interaction will occur, in
conjunction with an intensifying upper level jet streak arcing
into New England. The overlap of these height falls, PVA, and
upper diffluence should produce an area of low pressure off the
SC/GA coast late D3, with moisture increasing near the low and
surging northward into a cold front moving through the OH VLY.
This should produce some light to moderate snow late D3 across the
eastern OH VLY, the Southern/Central Appalachians, and into the
Mid-Atlantic where WPC probabilities for more than 2 inches are
above 40% in the terrain, but and around 10% in the foothills and
lower elevations. While beyond this period, it is becoming
increasingly likely this system could develop into a strong
coastal low during D4, with heavy snow impacting much of the
Mid-Atlantic and Northeast Friday night and into the weekend.

Weiss


~~~ Key Messages for Jan 28-30 East Coast Winter Storm ~~

- Confidence is increasing that a significant winter storm will
create considerable impacts Friday through the weekend from the
Mid-Atlantic through the Northeast.

- Heavy snow is most likely in parts of New England. Heavy snow is
still possible farther south along the East Coast, including the
major I-95 metro areas from New York City to Washington, D.C., but
that is more uncertain at this time.

- Significant coastal impacts are possible in the Northeast,
including coastal flooding and beach erosion. Additionally, strong
winds may cause blowing snow and some damage.

- Hazardous travel conditions are likely in parts of the region.
Please continue to monitor for updates, and check your local
forecast at weather.gov


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


Weiss