Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
306 AM EST Sun Dec 25 2022

Valid 12Z Sun Dec 25 2022 - 12Z Tue Dec 27 2022

...Arctic air enveloping much of the eastern two-thirds of the U.S. will
be slow to moderate...

...Lake-effect snows downwind from Great Lakes with locally blizzard
conditions will slowly become less intense...

...Heavy mixed precipitation to impact the Pacific Northwest followed by
snow across the Northern Plains to the Midwest...

The large and robust low pressure system lifting through southeastern
Canada is expected to slowly progress eastward while weakening. On the
backside of this departing low will be blustery West/Northwesterly winds
that will continue to filter in cold Canadian air to the eastern
two-thirds of the nation, with only slow moderation of temperatures into
Monday. With the persistent Arctic blast under the tight pressure gradient
on the back side of the low pressure system over the open warm waters of
the Great Lakes, lake-effect snows with local blizzard conditions may
linger into Christmas Day.  Storm totals may reach 2-4 feet in the favored
snow belts. Conditions are expected to slowly improve as the system
weakens; however, traveling in these conditions will be extremely
dangerous in the most intense snow bands.

The life-threatening cold temperatures and in combination with dangerous
wind chills will create a potentially life-threatening hazard for
travelers that become stranded, individuals that work outside, livestock
and domestic pets. If you must travel or be out in the elements, prepare
for extreme cold by dressing in layers, covering as much exposed areas of
skin as possible and pack winter safety kits in your vehicles. In some
areas, being outdoors could lead to frostbite in minutes. Ensure outdoor
animals and livestock have sufficient shelter.

Across the western states temperatures are forecast to stay milder than
seasonal average. An Alberta clipper forming along the boundary between
the two air masses will deliver a period of snow across the Northern
Plains into the Midwest during the next couple of days, with areas of
rain/freezing rain over parts of the Northern High Plains on Christmas. 
Meanwhile, warmer and increasingly moist air streaming inland across the
Pacific Northwest will overrun cold air trapped in valleys which could
yield mixed precipitation or significant icing. Freezing rain potential
will extend to northern Idaho and western Montana as well. By Christmas
night into Monday, the next low pressure system coming from the Pacific
will deliver the next surge of moisture toward the Pacific Northwest and
then into northern California. This system will usher in an atmospheric
river so there may be locally enhanced precipitation that may lead to
excess runoff. The potential threat for local flash flooding will continue
to be monitored.

Campbell/Kong


Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php