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Say goodbye to the polar vortex: Gradual warming ahead

Temperatures remain dangerously cold across the Midwest and Northeast but the polar air is finally beginning to retreat.

The worst of the brutally cold "polar vortex" that plunged millions of Americans into a deep freeze was over Wednesday, forecasters said, and though temperatures were still below normal gradual warming was on the way.

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The weather system was receding north, having set new record low temperatures in 50 cities on Tuesday.

Minneapolis-St. Paul, Minn., spent 62 consecutive hours below zero. Chicago spent 37 hours below that threshold, including 29 hours in double digits below zero, according to The Weather Channel.

Freezing temperatures were still widespread across the upper eastern half of the United States for much of Wednesday — with the upper Plains below zero — but most areas affected by the extreme cold were beginning to thaw. Conditions are expected to be back to normal by Friday.

"It’s still going to be below average for most of the East but the worst of the Arctic outbreak is over with," said Guy Walton, a meteorologist at The Weather Channel.

"It will be getting dramatically warmer from today. It is still as much as 20 degrees below average in the Northeast but by Thursday temperatures will be almost back to normal."

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Temperatures plummeted as a whirlpool of frigid, dense air known as a "polar vortex" descended on much of the United States.

The polar vortex is a cyclone of high winds which usually sits at the North Pole. Changes in the jet stream have meant these winds traveled south, encasing much of the U.S. and Canada in ice throughout the week.

With warmer air displacing the cold air, the chances of snow across the Great Lakes will diminish into Thursday, and light rain was forecast to move up the East Coast, according to the National Weather Service.

The thaw will be gradual, Weather.com reported, but temperatures should go above freezing and stay there for nearly all of the United States by Thursday afternoon. The Northeast should see temperatures in the mid 40s.

Highs temperatures in the Plains states and Northern New England will be in the 20s, typical in those areas for this part of the year.

In Maryland – where at least six people have died from the extreme weather – a 28-year-old Baltimore man was found dead  behind an elementary school  before classes started on Wednesday. Police told NBC station WBAL-TV that he died of hypothermia. The severe cold also burst several pipes in the region.

Authorities in Indiana rescue a dog that had been left outside in sub-zero weather, and was found frozen to the ground. WFIE's Nick Lagrange reports.

Almost 7,000 flights were canceled in the U.S. on Monday and Tuesday. Things appeared to be improving on Wednesday, with 542 cancellations by 4 a.m. ET, according to FlightAware.

Amtrak said Wednesday that its service along the Northeast corridor would be back to normal on Thursday after days of reduced operations because of the snow and cold.

All 50 states dipped below 32 degrees at some point Tuesday — even Hawaii, where it was 25 at the top of the Mauna Kea volcano, which is normally right at the freezing line this time of year.

Arctic temperatures continue to put on the freeze on millions of people in the country, shattering records in many southern states. NBC's Dylan Dreyer reports from Minnesota.

Schools and businesses closed for a second day. Single-digit temperatures were recorded at sunrise as far south as Georgia and Alabama, and parts of Minnesota were as cold as 25 degrees below zero.

A 118-year-old record was shattered in Central Park in New York, where it was 4 degrees, the coldest reading on the books for Jan. 7 and the coldest at any time since January 2004. Factor in the wind, and it felt like 31 below in Chicago, 16 below in New York and 45 below near the U.S.-Canadian border in Minnesota.

At least 17 deaths were blamed on the severe weather since snow and bitter cold started punishing the Midwest late last week, according to counts by NBC News, NBC stations and The Weather Channel.

In Chicago, a peacock that escaped from a suburban zoo on Tuesday died after spending 90 minutes outside during sub-zero weather. Brian Mangiaracina, park and division manager for Randall Oaks Barnyard Zoo, told NBCChicago.com that the fire department lifted a zoo worker up to rescue the peacock, known as Blue, after its feet became frozen to a tree branch in minus-12 temperatures. The bird died overnight.

NBC News' M. Alex Johnson contributed to this report.

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