The record-breaking polar air that has made the Midwestern U.S. shiver over the past few days spread to the East and South on Tuesday, setting record low temperatures 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.

The morning weather map for the eastern half of the U.S. looked like an algebra worksheet: lots of small, negative numbers. In fact, the Midwest and the East were colder than much of Antarctica.

The big chill started in the Midwest over the weekend, and by Tuesday, it covered about half of the country. In New York City, the high was expected to be -12 C; in Boston, around -8 C.

Polar vortex?

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."

Across the South, records were shattered like icicles. Birmingham, Alabama, dipped to a low of -14 C), breaking the record of -11.7 C set in 1970. Atlanta saw a record low of -14.5 C. Nashville, Tennessee, got down to -16.7 C, and Little Rock, Arkansas, fell to -13 C. It was just -17 C at Washington Dulles International airport, eclipsing the 1988 mark of -13 C.

The deep freeze dragged on in the Midwest as well, with the thermometer reaching -24 C overnight in the Chicago area and -25.5 C in suburban St. Louis.

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.

The cold turned deadly for some: Authorities reported at least 21 cold-related deaths across the country since Sunday.

The worst should be over in the next day or two. Warmer weather — at least, near or above freezing — is in the forecast for much of the stricken part of the country.

On Tuesday, many schools and day care centres across the eastern half of the U.S. were closed so that youngsters wouldn't be exposed to the dangerous cold. Officials opened shelters for the homeless and anyone else who needed a warm place.

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.

In New Orleans, which reported a low of -3 C, hardware stores ran out of pipe insulation.

A pipe burst in an Atlanta suburb and a main road quickly froze over. In downtown Atlanta, a Ferris wheel near Centennial Olympic Park that opened over the summer to give riders a bird's eye view of the city closed because it was too cold.

Sabres-Canes game postponed

The Hurricanes have been shut down by a blizzard.

The NHL has postponed the game scheduled for Tuesday night in Buffalo between the Sabres and Carolina because of a snowstorm in western New York. 

A makeup date has not been determined. The postponement comes with Buffalo dealing with a wintry blast of frigid temperatures, heavy winds and blinding snow that has forced the closure of most major roadways. 

Farther south in Pensacola, Florida, a Gulf Coast city better known for its white sand beaches than frost, streets normally filled with joggers, bikers and people walking dogs were deserted early Tuesday. A sign on a bank flashed 19 F (-7 Celsius). Patches of ice sparkled in parking lots where puddles froze overnight.

The continental U.S., when averaged out, reached a low of -10 C overnight Monday, according to calculations by Ryan Maue of Weather Bell Analytics.

An estimated 190 million people in the U.S. were subjected to the icy blast, caused by a kink in the "polar vortex," the strong winds that surround the North Pole.

In Chicago, it was too cold even for the polar bear at the Lincoln Park Zoo. While polar bears can handle below freezing cold in the wild, Anana was kept inside Monday because she doesn't have the thick layer of fat that bears typically get from feeding on seals and whale carcasses.

With files from CBC News