Winter started unusually mild across much of the Lower 48 in December, but some of the coldest air to visit the Northeast in three years is spilling south to kick off the workweek. At least 9 million Americans could awaken Tuesday to temperatures below zero, with temperatures 15 to 20 degrees or more below average.

Wind chill advisories and warnings blanket much of the Northern Tier, Upper Midwest and Northern New England, where temperatures could be downright dangerous. Wind chills in northern Maine and along the Canadian border could plummet to minus-40 degrees.

While relatively few records are in jeopardy, unusual mildness in the past several years means the encroaching chill will be the coldest since January 2019 for a number of cities in the Northeast. It comes in stark contrast to December, which featured four record-setting pulses of warmth and severe weather to parts of the southern and central United States.

The cold looks to be brief and only last into Wednesday, but there are signs that a busy pattern could be in the cards, with more cold and winter weather in the hopper for the eastern United States.

Frigid air overspreading Great Lakes, Eastern United States

The atmosphere seemed to have a case of the Sunday night blues when a band of rain brought dreary conditions along the Interstate 95 corridor from the Carolinas to New England. Severe weather, including a couple of tornadoes, accompanied the instigating cold front in Alabama, but the front has since cleared the coast and moved into the open Atlantic. Behind, sunny skies and a cold air mass are building in from the northwest.

Boston is predicted to dip to 7 degrees on Monday night, about 16 degrees below its average low for the date. It’s nowhere near the record of minus-4 set back on Jan. 11, 1893, but it’s still the coldest since Jan. 31 of last year. If the temperature manages to fall below 7 degrees, it will go down as Boston’s coldest reading since Jan. 5, 2018.

Rutland, Vt., could make it to 6 degrees below zero on Tuesday morning, and peak Tuesday afternoon with a high of only 2 degrees. Some areas in Upstate New York near the Canadian border could awaken to readings in the double digits below zero early Tuesday, with afternoon highs between 5 below and 5 above zero. Boston’s projected high Tuesday is only 12 degrees.

D.C. is only anticipated to hit 29 degrees Tuesday afternoon, which would be the coldest afternoon high there in nearly three years.

Satellite imagery depicted tendrils of cloud cover and even lake-effect snow reaching down from the northwest as the frosty air mass became established.

Freezing conditions could surge all the way down to the Gulf Coast on Tuesday morning in Alabama, with the possibility of “Arctic sea smoke,” a form of fog, being visible over the waters around sunrise. It forms as cold air pours south and condenses the moisture trapped in the shallow layer of humid air in contact with the ocean.

The same instigating cold blast will bring subzero readings to the entirety of Wisconsin and most of Minnesota. Actual air temperatures in northern Minnesota could approach minus-20, with wind chills as low as 45 degrees below zero. The National Weather Service hoisted a wind chill warning, writing that “the dangerously cold wind chills could cause frostbite on exposed skin in as little as 10 minutes.”

Chicago began Monday morning at 15 degrees but was expected to see temperatures decline during the day as cold air advection, or the arrival of frigid air, counteracts daytime heating. Windy City temperatures could fall to near zero Monday night.

The air mass settling into place across the Northeast has ties to Nunavut, Canada.

While the core of the cold looks to stick around over the Midwest for only for a day, it’ll linger in northern New England through Wednesday. Then the cold will relent, but signs point to a favorable pattern for wintry weather as we head deeper into January.

A lobe of Arctic air at high altitudes, essentially a piece of the polar vortex, looks to become established over the Upper Midwest and north-central United States. That will lend itself to bringing extreme cold there and setting the stage for clashing air masses and potential snowstorms along its eastern periphery, which will brush against the Atlantic shoreline into the weekend. It’s still unclear whether storminess will wallop the East Coast or remain over the ocean through early next week.

Lake-effect snows in New York state

The cold air blowing lengthwise along Lakes Erie and Ontario will generate lake-effect snows thanks to the contrast between mild surface water temperatures and chilly air above. Any moisture evaporated into the atmosphere will be transformed into snowfall in a narrow band only a few miles across, but thundersnow and snowfall rates topping 2 to 3 inches per hour are likely in this band.

Totals of up to two feet are possible across New York’s Tug Hill Plateau through Tuesday morning, at which point the wind direction, which is now parallel to lines of equal air pressure between a low banked to the north and high pressure to the south and east, will change. That will spell an end to lake-effect snow squalls.

“The lake effect snow band was nearly stationary,” wrote the National Weather Service in Buffalo about the snow band emanating from Lake Ontario. “This lake effect snow band is producing extremely heavy snow.” The Weather Service also warned of visibilities below a quarter-mile.

A stormy pattern ahead

More snow could be in the cards across a broader swath of the Northeast. The upcoming weather pattern for the remainder of January, while uncertain, favors an active continuation of winter that could brew more snowstorms and wintry weather in the East. One atmospheric scientist, Judah Cohen, is calling it “the most active midwinter pattern in the Eastern U.S. since 2014 [and] 2015,” when Boston measured more than 80 inches of snow in a three-week span and tallied 110.6 inches for the season.

January 2022 has already gotten off to an impressive start with regard to snow. Washington picked up 6.9 inches of snow on Jan. 3 and another 2.7 during the predawn hours Friday, totaling 9.6 inches over the course of five days. The seasonal average is about 14 inches, meaning the nation’s capital recorded most of an entire season’s worth of snowfall in a week. Friday featured an overperforming system that delivered a surprise eight inches to New York City.