Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EST Wed Jan 26 2022

Valid 00Z Thu Jan 27 2022 - 00Z Sun Jan 30 2022

...Central Rockies...
Day 1...

A shortwave will dig south out of Alberta Canada around an
amplified but short wavelength ridge centered along the Pacific
coast. This feature will sharpen as it dives towards the Four
Corners Thursday aftn, and will push a decaying front southward
into the Front Range and across the High Plains. The overlap of
height falls, fgen atop the weakening boundary, and modest LFQ
upper diffluence ahead of a polar jet streak will combine to
produce a swath of precipitation from southern WY through CO and
into northern NM. While moisture is somewhat limited, mid-level
deformation collocated with the saturated DGZ will help squeeze
out snowfall, which at times may be briefly heavy as noted by HREF
probabilities for 1"/hr as high as 30%. Total accumulation will be
limited, with WPC probabilities for 4+ inches less than 5%, but
the heavy rates could lead to some impactful accumulations of a
few inches, including along the I-25 corridor and the Palmer
Divide.


...Great Lakes/Northeast...
Days 1-2...

Broad cyclonic flow centered around a mid-level low over the
Hudson Bay will be reinforced by a cold front moving across the
Great Lakes Thursday accompanying a modest shortwave moving
overhead. This front will produce light precipitation along and
ahead of it, with the environment in its wake characterized by CAA
favorable for Lake Effect Snow (LES) in the typical N/NW snow
belts. On Friday, a secondary shortwave with greater intensity
will move across the Lakes driving amplification of the trough
leading to continued CAA but with a more northerly low-level wind
component. This will additionally produce LES, but in the more
northerly-favored belts.

For D1, the heaviest snowfall is likely across the U.P. and
northwest L.P. near Traverse City where WPC probabilities are high
for 2+ inches but low for more than 4 inches, limited by a
relatively shallow DGZ. By D2, LES will become more widespread,
extending downwind of Lake Ontario and Lake Erie, with more
impressive snowfall possible south of Lake Michigan near Gary, IN.
WPC probabilities for 4+ inches are moderate into the Tug Hill
Plateau east of Lake Ontario, as well as into NW Indiana where a
single convergent band may develop along Lake Michigan.


...Southern Appalachians through the Mid-Atlantic...
Days 2-3...

Shortwave energy rounding the expansive eastern CONUS trough will
dig out of the Northern Plains Friday, while southern stream
energy drops through the Four Corners region and towards West
Texas. These features will attempt to phase over the Southeast
Friday night, which when combined with increasing upper diffluence
within the RRQ of an intensifying jet streak arcing into New
England, will drive cyclogenesis off the SC/NC coast. This surface
low is then likely to explosively deepen in response to an
increasingly coupled upper jet structure and the mid-level trough
tilting negatively and closing off. While guidance still features
a wide array of timing/placement solutions, the trend with the
daytime guidance has been for a slightly more eastward track of
the surface low, likely due to a slower ejection of the southern
stream energy shifting out of New Mexico on Friday.

As the low consolidates late Friday into Saturday, moisture will
begin to advect northward as the WCB develops and spreads rich
theta-e air northward and up the coast. At the same time, a cold
front dropping southeast will produce enough ascent to create
light to moderate snowfall across the Appalachians and
Mid-Atlantic late Friday, with some upslope enhancement leading to
the greatest accumulations. WPC probabilities late Friday/Friday
night (D2.5) are 10-30% for 4+ inches in the Southern and Central
Appalachians. Thereafter, the precipitation will become
increasingly dependent on the track of the low with a large shield
of rain and snow shifting northward and westward around the
surface low. This will likely manifest as a corridor of heavy
snowfall within the warm conveyor belt across the eastern
Mid-Atlantic and into New England, with backside deformation
snowfall likely developing down the coast as far as NC in the wake
of the low. Snow rates will likely exceed 1"/hr at times in many
locations, with 2"/hr possible in eastern New England. WPC
probabilities are currently high for 6+" from the DelMarVa
Peninsula northeast through Long Island and into much of eastern
New England. More than 12 inches of snowfall is possible across
eastern MA and coastal ME, including Boston, MA and Portland, ME.
Additional heavy snow is likely beyond this forecast period across
much of Maine Saturday night into Sunday, with the heaviest likely
along the coast.

It should be noted that as well that here has been a shift
eastward today in the guidance, and the WPC PWPF may adjust lower,
especially across inland portions of the region with later updates.


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

Weiss


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

- A winter storm is likely to create significant impacts across
New England Friday night through Sunday. Notable impacts may also
extend south along the East Coast through North Carolina.

- Across New England, heavy snow and strong winds are likely which
could lead to blowing snow, scattered power outages, and some
damage. Additionally, significant coastal impacts are possible,
including coastal flooding and beach erosion.

- Farther south from New York City through Washington, D.C., and
into northeast North Carolina, moderate to heavy snow is possible
which could create hazardous travel conditions.

- This forecast continues to evolve. Please check for updates and
your local forecast at weather.gov