Frigid air poised to invade U.S. during Christmas week
Weather models are in strong agreement that blasts of frigid air will plunge into the northern Plains, Midwest and eastern United States in the days leading up to Christmas. Some of this air – 30 or more degrees below average – might be the coldest in late December in at least two decades.
At the same time, there are increasing odds of significant winter storminess in the eastern half of the nation between Wednesday and Christmas Eve. While far from a lock, Mother Nature may deliver a white Christmas for a swath of the Midwest and eastern United States.
The frigid weather and possibility of snow will coincide with a peak time for holiday travelers. At roughly a week out, it’s not possible to forecast exactly where a storm might form and what areas will see snow or rain or remain dry. But between Dec. 22 and 24, the chance of a significant storm between the Midwest and East Coast is above normal.
The primary setup for our potential outbreak of wintry weather involves strong high pressure building over the eastern Pacific Ocean toward the Alaska Aleutian Islands. That high acts as a force field, deflecting the jet stream around it. The jet – which separates frigid and more mild air – will bulge toward the Arctic Circle in central North America before crashing southward over the central and eastern United States.
We can glance at a model of the trajectories of air parcels in the atmosphere for clues about the origins of next week’s air mass. If we run the model for Christmas Eve in the Midwest, it traces the air back to Nunavut, Canada, between the Northwest Passages and Baffin Bay, adjacent to Greenland.
The initial blast of cold will drive southward into the northern Rockies and northern Plains on Monday and Tuesday, reaching the Great Lakes Tuesday into Wednesday. Some of the coldest areas near the border with Canada could see temperatures 30 to 40 degrees below normal, meaning highs around minus-10 and lows from minus-20 to minus-30. Subzero temperatures could reach as far south as the central Plains.
The core of the cold will probably remain over the north central United States through midweek, although temperatures 10 to 20 degrees below normal could reach parts of the South and the eastern United States late in the workweek.
A second, reinforcing blast of cold may dive into the northern Plains and Upper Midwest Wednesday and Thursday, pushing frigid air even farther south and east.
Minneapolis should expect lows well below zero while Chicago may see highs only in the teens for much of the second half of next week.
By Christmas Eve and Christmas Day, much of the eastern half of the country may see temperatures 10 to 30 degrees below normal.
There are signs a third shot of frigid air could enter the northern Plains around Christmas Day before barreling south and eastward about 10 days from now.
The National Weather Service’s Climate Prediction Center places high odds of below average temperatures in the central and eastern states both 6 to 10 and 8 to 14 days into the future.
The potential for snowfall will stretch from the Plains to the East Coast during the second half of next week. Here’s what we know:
Central states: As the jet stream dives south over the Plains, a disturbance embedded within that flow could cause some snow to break out over the central and northern Plains before sweeping across the Midwest and Tennessee and Ohio valleys. The exact of track of any disturbance is still unclear, as is the location of the rain/snow transition line; the timing would probably be around Wednesday into Thursday.
Mid-Atlantic and Northeast: The disturbance that could bring snow to the central states could evolve into a major East Coast storm. It would have plenty of jet stream energy to feed off and could draw abundant moisture from the Atlantic Ocean. However, it’s still highly uncertain if and where a coastal storm might form and what areas will be hardest hit. The timing of this storm would probably be between Thursday and Christmas Eve.