Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 AM EST Sat Dec 24 2022

Valid 12Z Sat Dec 24 2022 - 12Z Tue Dec 27 2022

...Great Lakes through the Interior Northeast...
Days 1-3...

...Dynamic system to slowly lift away from the Great Lakes but
with lingering effects through the weekend...

Still intensifying low slowly lifts north to the Hudson Bay today 
deep upper low. With strong high pressure edging east over the
northern Plains, the pressure gradient will remain strong with
high winds continuing today over the Great Lakes, supporting
lake-effect blizzards. With 850mb temperatures -12C to -24C (core
of the cold across the Ohio Valley), plenty of delta T between the
still mild lakes and 850mb will maintain multi-bands over the U.P.
and Lower Michigan but intense single bands off Erie/Ontario on SW
flow. Such strong winds may limit SLRs despite the strong lift
(though the column is mostly colder than the DGZ), but three-day
additional snow amounts are still for a few more feet in favored
locations including very near Buffalo on rates of 2-3"/hr. WPC
probabilities for at least 12 additional inches are limited to Day
1 in the U.P., but are high through Day 2 near the Tug Hill and
near Buffalo. Lake effect will wind down starting late Sunday and
into Monday from the Upper Lakes initially and into Ontario last.


...Pacific Northwest...
Days 1-3...

...Significant to damaging freezing rain event continues...

Arctic air remains in place over much of the Interior PacNW with
intrusions of cold air toward sea level through gaps such as the
Columbia Gorge countering a slow-moving warm front trying to
advance inland. The next shortwave trough approaches the BC coast
today with an atmospheric river surging across the WA/OR coasts.
Milder Pacific flow will encompass the area, further raising snow
levels along and west of the Cascades well above pass level. Areas
east of the Cascades will be slower to moderate, with a lingering
light icing threat through Sunday. Farther east, moisture will
wring out over northern Idaho and northwestern Montana deep into
the cold air. Then the next wave enters the region Monday night
with height falls leading to lower snow levels.

...Northern Plains to the Mid-Mississippi Valley...
Days 1-3...

An Alberta Clipper Canada shifts southeast down the Northern Great
Plains Saturday night/Sunday, reaching the Mid-Mississippi Valley
by Monday morning before being sheared apart by a reinforcing
trough late Monday, greatly weakening the wave before it reaches
the Mid-Atlantic. A modest push of milder air atop the cold
surface layer in advance of the wave will support a chance of
light icing on the southern/western side of the precip shield with
moderate Day 1/2 probabilities for measurable icing stretching
from eastern MT through western MO. A band of locally moderate
snow is expected from North Dakota southeastward into the Midwest
on the order of a few inches. WPC probabilities of at least 4
inches of snow are around 20% over eastern ND with moderate Days
2/2.5 probabilities for 2 or more inches stretching southeast from
there through southern IL.


Jackson


Key Messages for Blizzard
--Blizzard Conditions from Strong Winds and Heavy Snow
A powerful winter storm will continue to produce snow across parts
of the Great Lakes and Northeast. Enhancement from the Great Lakes
will aid in producing 2-4 foot totals in the favored snow belts.
Even where lesser accumulations occur, heavy snow rates combined
with wind gusts over 40 MPH will result in blizzard conditions.

--Widespread Potentially Damaging Winds & Ground Blizzards
Even away from the heavy snow, this powerful storm will bring
widespread wind gusts over 40 MPH to a large portion of the
central and eastern U.S. into Sunday. In some spots, wind gusts
could approach or exceed 60 MPH resulting in damage and power
outages. These winds atop existing snow cover will produce ground
blizzards.

--Extremely Dangerous Travel with Whiteout Conditions
Where blizzard conditions occur, expect periodic whiteouts with
near-zero visibility and considerable blowing and drifting of
snow.
Traveling in these conditions will be extremely dangerous, to at
times impossible.

--Life-threatening Cold Temperatures
Dangerous wind chills will create a potentially life-threatening
hazard for stranded travelers. If you must travel, prepare for
extreme cold. In some areas, being outdoors could lead to
frostbite in minutes. Ensure outdoor animals and livestock have
sufficient shelter.

--Coastal and Inland Flooding Threat for the Northeast
Heavy rain falling onto a melting snowpack will enhance flooding
impacts. Moderate to isolated major coastal flooding is forecast
due to strong onshore winds.  Rapidly falling temperatures on the
backside of the storm could cause flooded areas to freeze in place.


Key Messages for Arctic Blast
--Dangerous Cold for Much of the U.S.
An Arctic cold front will continue to push through the remainder
of the eastern U.S. tonight, with frigid temperatures and gusty
winds expected to produce dangerously cold wind chills across much
of the central and eastern U.S. this holiday weekend. 

--Increased Danger if Power Outages Occur
The danger of the cold will be increased if any power outages
occur due to the widespread gusty winds around the winter storm
system.

--Cold Weather Safety
In the event of a power outage...
----Candles and space heaters are a fire risk. Stay warm by
bundling up and keeping doors closed, and placing towels in cracks.
----Practice portable generator safety, and donâ€t use camp
stoves or unvented heating devices to heat indoors. Only use them
outdoors at least 20 feet away from doors, windows, and garages to
avoid carbon monoxide poisoning.
----Bring pets inside and check on your neighbors and the
vulnerable to make sure they are safe.
----Protect exposed plumbing and pipes.

--Moderating Temperatures Next Week
Temperatures are expected to gradually warm early next week, with
seasonal to above-normal temperatures likely by midweek.