The polar vortex that spun arctic temperatures down into southern Canada and even the southern United States got back to its usual job today of confining cold to the planet's ice cap.

"Today, we're at the ready to start saying goodbye to the polar vortex, as temperatures start to improve across the country," said CBC meteorologist Jay Scotland.

The arctic blast that created a deep freeze across North America this week eased its grip on much of Canada and the U.S. Wednesday, with winds calming and the weather warming slightly a day after temperature records — some more than a century-old — shattered up and down the Eastern Seaboard.

Cancelled flights

Total cancellations within, into or out of the United States had fallen to 570 as of 6:20 a.m. ET today, according to the flight-tracking website FlightAware.com. That was well down from comparable numbers Monday and Tuesday. For a more visual look, check the Misery Map.

Temperatures continue to rise today across the Prairies, but it was still a chilly start to the east through Saskatchewan and Manitoba, Scotland said.

To the west, much of southern Alberta was forecast to be warm Wednesday, as a strong westerly (Chinook) winds roared out of the Rockies. Calgary expected a high of 3 C as a result.

In Manitoba, wind-chill warnings were still in effect in the north — Lynn Lake and Thompson — and Winnipeg remained cold at –22 C, but will get warmer Thursday.

In the U.S., where Atlanta saw a record low of –14 C Tuesday, the forecast Wednesday was for sunny skies and 5 C. 

Polar vortex?
Polar vortex graphic

The polar vortex refers to winds that whip around the polar ice cap, trapping Earth's coldest temperatures there.

Its deterioration with global warming, however, can send arctic weather south into areas as far away as the southern U.S. and Europe, according to National Oceanic and Atmospheric Administration scientists.

"When the polar vortex … breaks down, this allows cold air to spill south, affecting the eastern United States and other regions," says NOAA's Dr. James Overland.

"This can result in a warmer-than-average arctic region and colder temperatures that may include severe winter weather events on the North American and European continents."

In the Midwest and East, where brutal polar air has lingered over the past few days, temperatures climbed but were still expected to be below freezing.

Buffalo, N.Y., was experiencing severe snowfall blowing in off Lake Erie, with winds of 45 km/h and 30 centimetres of snow expected.

With the bitter cold slowing baggage handling and aircraft refuelling, airlines cancelled more than 2,000 flights in the U.S., bringing the four-day total to more than 11,000.

On Tuesday, the mercury plunged into the single digits and teens, from Boston and New York to Atlanta, Birmingham, Nashville and Little Rock — places where many people don't know the first thing about extreme cold.

21 cold-related deaths

"I didn't think the South got this cold," said Marty Williams, a homeless man, originally from Chicago, who took shelter at a church in Atlanta. "That was the main reason for me to come down from up North, from the cold, to get away from all that stuff."

The cold turned deadly for some: Authorities reported at least 21 cold-related deaths across the United States since Sunday, including seven in Illinois and six in Indiana. At least five people died after collapsing while shovelling snow, while several victims were identified as homeless people who either refused shelter or didn't make it to a warm haven soon enough.

In Missouri on Monday, a one-year-old boy was killed when the car he was riding in struck a snow plow, and a 20-year-old woman was killed in a separate crash after her car slid on ice and into the path of a tractor-trailer.

In a phenomenon that forecasters said is actually not all that unusual, all 50 states saw freezing temperatures at some point Tuesday. That included Hawaii, where it was –8 C atop Mauna Kea, a dormant volcano.

It was –17 C in Reading, Pa., and –17 C in Trenton, N.J. New York City plummeted to –15 C, beating a record of –14 C set in 1896.

Chilly records

"It's brutal out here," said Spunkiy Jon, who took a break from her sanitation job in New York to smoke a cigarette in the cab of a garbage truck. "Your fingers freeze off after three minutes, your cheeks feel as if you're going to get windburn, and you work as quick as you can."

Farther south, Birmingham, Ala,, dipped to a low of –14 C, four degrees colder than the old mark, set in 1970.

The big chill started in the Midwest over the weekend, caused by a kink in the "polar vortex," the strong winds that circulate around the North Pole. The icy air covered about half the country by Tuesday, but it was moving north, returning more normal and warmer weather to most of the U.S..

The deep freeze dragged on in the Midwest. More than 500 Amtrak passengers were stranded overnight on three Chicago-bound trains that were stopped by blowing and drifting snow in Illinois. Food ran low, but the heat stayed on.

On Tuesday, many schools and daycare centres across the eastern half of the U.S. were closed and officials opened shelters for the homeless and anyone else who needed a warm place. 

With files from CBC News