Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
351 PM EST Sun Nov 13 2022

Valid 00Z Mon Nov 14 2022 - 00Z Thu Nov 17 2022

...Great Lakes...
Day 1...

The post-frontal lake effect snow machine will taper off from west
to east across the Great Lakes this evening through Monday as an
approaching trough switches the wind direction to
southerly/southeasterly. Decent single band setups off Lakes Erie
and Ontario have the potential to bring 2-4" to preferred places.
The heaviest band is still progged around Syracuse which will
overcome warm sfc conditions this evening.

...Northern Maine...
Day 1...

A shortwave trough currently taking on a negative tilt over the
Interior Northeast will continue to promote low level cyclogenesis
and a tightening 850mb frontogenesis field will act to focus a
narrow band of heavy snowfall to the 850mb front's west over far
northern Maine. Day 1 WPC snow probabilities feature a 30-50%
chance for >8" of snowfall in Aroostook county. The WPC Snowband
Probability Tracker based on the 12Z HREF continues to depict CAM
members with up to 2"/hr snowfall rates this evening up there. As
the surface low deepens over Quebec early Monday morning, heavy
snow could contain strong gusts as well, leading to near zero
visibility at times. Snow will exit to the northeast by
mid-morning Monday.

...Southern Rockies, South-Central Plains, Upper Mississippi
Valley, and Great Lakes
Days 1-3...

A positively-tilted southern stream low/trough over AZ will open
as it crosses the southern Rockies tonight then take on a negative
tilt Monday as it lifts over OK and gets absorbed into a parent
low over the Red River of the North. An influx of 700mb moisture
combined with diffluent 250-500mb flow out in front of the trough
will foster period of heavy snow in the southern Rockies tonight
where WPC probs are moderate for 6 or more inches in terrain
mainly on the NM side of the border with CO.

A developing 850mb low over the TX Panhandle will tap into rich
850mb moisture flux that is advected north through Oklahoma into
Kansas. SW to NE oriented snow bands with the potential for
1-2"/hr snow rates are progged by the 12Z HREF Monday morning
across the OK Panhandle into west-central KS. The snow band risk
area then broadens in the afternoon with some bands continuing
east over KS and others developing over western OK and shifting
east over central OK. The mid level trough becomes less sharp as
it is absorbed into the parent low that evening with an inverted
trough developing up the MS Valley from a Gulf Coast sfc low to a
trough in MN which is east of the parent upper low. This makes for
a broad snow snow risk area Monday night from AR through MN with
generally light amounts though the threat for continued embedded
moderate bands does persist from KS into MO.

Farther north, the parent upper low over south-central Canada/Red
River of the North will direct creation of the inverted trough
Monday night and a strong dome of high pressure over southern
Canada and the northeastern U.S. will cause an elongated fetch of
southeasterly-to-easterly flow across the Great Lakes. The initial
upper low will help to produce periods of snow in the Upper
Mississippi Valley and northern Plains Monday morning. At the same
time, ESE 850mb flow over the western half of Lake Superior will
upslope into the Minnesota Arrowhead and focus heavier snowfall
bands there. Day 1.5 WPC probabilities for >6" of snow are 40 to
60% for particularly the northern half of the North Shore.
Continued snow expected there through Tuesday night continues to
bring 48-hour WPC probabilities for >12" of snowfall up to 10-30%.
There are accumulating snow chances across the Upper Midwest under
the upper low Monday afternoon into Wednesday with some 10%
probabilities for 6 or more inches near the MN/WI border and over
northeast WI through Tuesday night.


Appalachian Chain and northern New England...
Days 2-3...

The upper level trough responsible for the heavy snow potential in
the south-central Plains Monday morning will make its way through
the Mid-South Monday night. As it does, the divergent left-exit
region of a 250mb jet streak will become positioned over the
southern Appalachians at first, then work its way up the spine of
the Appalachians and the East Coast through Tuesday. This setup
favors a surface low tracking across the Southeast Tuesday night
and off the Mid-Atlantic coast by early Wednesday morning which
along with a dome of high pressure over southeast Canada leads to
cold air damming (CAD) over the Mid-Atlantic and Northeast by
Tuesday.

The leading warm air advection precip lifting up from the
Southeast Monday night and across the Mid-Atlantic/central
Appalachians Tuesday looks to have a super-freezing warm nose soon
after precip onset at least south of the Mason-Dixon line. So the
question becomes more about rain vs sleet/freezing rain Tuesday
morning/midday. The setup looks good for radiational cooling
Monday night allowing freezing rain and a light glaze of nice
generally west from the Blue Ridge where there are 20-30% Day 2
probs for over a tenth inch of ice mainly along the crest of the
Appalachians from western NC through the Allegheny Highlands and
Potomac Highlands.

A reinforcing shortwave promotes further low level cyclogenesis
Tuesday night through Wednesday as the sfc low tracks northeast
from Cape Hatteras just off the Northeastern Seaboard. This
results in a developing Nor'Easter with a rain/mix line just
interior to the Northeast coast and swaths of snow farther inland.
The day 3 freezing rain probs for a tenth inch or more are 10 to
30% over the Catskills to the south-central Hudson Valley and
Berkshires while snow probs for 6 or more inches are 10 to 30%
over the Adirondacks, Greens, and Whites with 4 inch probs
extending into the Champlain Valley.

Jackson