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BOSTON — Bitter cold set in after a major winter storm blanketed a wide swath of the country in snow, sleet and rain over the weekend, creating dangerously icy conditions that promise to complicate cleanup efforts and make travel challenging on Martin Luther King Jr. Day.

Some of the coldest temperatures felt so far this season across the Midwest and Northeast were expected to plunge further early Monday.

Wind chills will bring temperatures into teens in the New York City area and down to minus 40 degrees Fahrenheit in upstate New York, the National Weather Service predicted.

6 AM UPDATE - Wind Chill NOW.

🚨FROSTBITE POTENTIAL🚨

Important information to empower you to make smart decisions here: https://t.co/ofkWricam0 pic.twitter.com/Q8QsItjYnf — Peter Hall (@PeteWeatherBeat) January 21, 2019

In New England, they'll fall to as low as 20 F below zero around Boston and as low as 35 F below zero in parts of Vermont, Maine and New Hampshire, the service said.

Temperatures across the Great Lakes, Ohio Valley and the Mid-Atlantic will drop 10 to 20 degrees Fahrenheit below average, the service said.

COLD AIR -- WIND CHILLS



With the air temps falling to the single digits - low teens. Gusty winds out of the north - gusting up to 30 mph...

Wind chill temps will FEEL LIKE 0º to -15º@NBCChicago pic.twitter.com/5qd8A3RaDi — Alicia Roman (@AliciaRomanNBC) January 20, 2019

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"It's life-threatening," said Ray O'Keefe, a meteorologist with the National Weather Service in Albany. "These are dangerous conditions that we're going to be in."

The freeze will follow the weekend's run-ins with power outages, canceled trains and planes, overnight stays at the airport and traffic jams.

Local officials warned residents to limit their time outside to prevent frostbite and to avoid treacherous travel conditions. They also said places could see strong wind gusts, flooding and further power outages.

A pedestrian in downtown Scranton, Pa., on Sunday. Butch Comegys / AP

Utilities in Connecticut reported more than 20,000 customers without power by Sunday afternoon.

Amtrak canceled trains across the Midwest and Northeast over the weekend, but promised full service would resume Monday. Boston's transit system urged commuters to allow 10 to 15 minutes of extra travel time and warned of icy conditions for pedestrians come Monday.

The storm — caused by the clash of an Arctic high-pressure system with a low-pressure system coming through the Ohio Valley — wreaked havoc on air travel and other forms of transportation all weekend.

More than 1,500 flights were canceled nationwide Sunday, according to FlightAware, a flight tracking company.

A flight information display shows cancelled flights at Logan International Airport in Boston on Sunday. CJ Gunther / EPA

Among the hardest hit was Boston's Logan Airport, where stranded passengers lingered Sunday as typically bustling security lines, ticketing counters and baggage claims were largely deserted.

The storm dumped 10 inches of snow in parts of the Midwest. It also caused a plane to skid on a slick runway at Chicago's O'Hare International Airport on Saturday, though no injuries were reported.

In Kansas, a snowplow driver was killed when his vehicle rolled over, and in southeastern Missouri, slippery conditions caused a 15-vehicle crash on Interstate 55 on Saturday.

One saving grace of the storm: heavily populated coastal communities from New York to Boston largely escaped major snowfall after days of sometimes dire predictions.

Manhattan saw mostly rain while places along Connecticut, Rhode Island and Massachusetts' coast recorded 2 to 5 inches of snow.

The bitter blast of Arctic air intensifies overnight. This is what it'll feel like as you're waking up on Monday morning: #NBC4NY pic.twitter.com/XVasrl7La9 — Erica Grow (@Erica4NY) January 21, 2019

Mountain regions saw significantly more, to the delight of ski resort operators.

New York's Adirondacks registered up to 20 inches while western Massachusetts' Berkshires saw as much as 10 and parts of northern New England were on track to approach 24 inches of snow.