CHICAGO – An historic and deadly polar vortex gripped a wide swath of the nation Wednesday, with temperatures plunging far below zero and wind chill numbers as extraordinary as they are dangerous.

Chicago’s temperature tumbled to 21 degrees below zero, a record for the date and closing in on the city’s all-time record of minus 27 set in 1985. The wind chill dipped to an even more startling 51 degrees below zero.

The National Weather Service said the temperature reached minus 28 degrees in Minneapolis, poised to break a record dating back more than 100 years. The wind chill: minus 49.

Wind chill temperatures in dozens of towns across Minnesota and North Dakota plummeted to 60 degrees below zero or less, the National Weather Service said. The early leader was Ely, Minnesota, with a very cool minus 70 degrees.

Frostbite can set in within five minutes in such temperatures, the weather service said.

“One of the coldest arctic air mass intrusions in recent memory is surging south into the Upper Midwest before spreading across much of the eastern two-thirds of the country,” the National Weather Service said, warning of “life-threatening wind chills, likely leading to widespread record lows and low maximum temperatures.”

Thousands of flights into and out of airports in the region were delayed or canceled, including more than 1,000 flights at Chicago airports alone.

Amtrak pulled the plug in Chicago, announcing the “extreme weather conditions and an abundance of caution” led the service to cancel all trains to and from the city on Wednesday. Short-distance services are also canceled on Thursday, Amtrak said.

Light rail was also a mess, with some suburban lines shutting down Wednesday. The Chicago Transit Authority, which shuttles about 1.6 million riders on a typical weekday, said it was experiencing significant delays.

Even the Postal Service took notice, announcing that due to concerns for the safety of its employees, mail won’t be delivered Wednesday in parts of at least 10 states.

At least four deaths were linked to the weather system, including a man struck and killed by a snow plow in the Chicago area, a young couple whose SUV struck another on a snowy road in northern Indiana and a Milwaukee man found frozen to death in a garage.

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Almost 40,000 homes and businesses were without power in Indiana, Illinois, 

Homeless shelters and warming centers were abuzz across the region. In Chicago, officials added 500 shelter beds and tapped more than 100 religious leaders to make calls and checks on senior citizens. Five Chicago Transit Authority buses were dispatched to give homeless people a place to warm up who might not want to go to a shelter.

“Everyone of us has a role to check on somebody who is maybe a neighbor on the block who is elderly, infirm or needs extra help,” Mayor Rahm Emanuel said.

The weather was headed east. New York’s forecast high for Thursday’s high was 16 degrees, with a wind chill of minus 15. The city Housing Authority activated its Situation Room, with heating response teams prepped to respond to heat and hot water emergencies. 

Philadelphia enacted “Cold Blue,” including 24-hour outreach to find people who are homeless and transport them to safe indoor spaces.

Pets were also a concern, Chicagoland Dog Rescue warned.

“Don’t leave your pets outside unattended in this weather, period,” the rescue organization warned on Twitter. “Make sure your gates are latched and your dog(s) cannot escape your yard.”

The weekend could finally bring relief. In Des Moines, Iowa, the temperature barreled down to minus 20 on Wednesday with a wind chill of minus 40. But Allan Curtis, a meteorologist with the Des Moines branch of the National Weather Service, said the temperature on Saturday could exceed 40 degrees above zero.

“It may as well be basketball shorts weather,” Curtis said.

Madhani reported from Chicago, Bacon from McLean, Virgina. Contributing: Austin Cannon, Des Moines Register; The Associated Press

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