Several thousands of flights are cancelled every day and stray air accidents have also been reported. Twentyone people have died of cold so far. One exposed to the the chill cold for extended periods in temperature 15 degrees F (minus 9.5 deg C) can develop frostbite and conditions of hypothermia leading to emergencies. Offices and schools are shut.

The snow storm is blasting even down south up to Alabama, where the temperature is in the negative of minus 13 deg C while up in north, Chicago recorded minus 26 deg C.

According to the US National Weather Service, most of Midwest, where temperatures have plummeted, is more than 98 percent snow-covered.

As the coldest air in 20 years is taking most of America into its grip, a debate is raging as to why the polar vortex, that has caused the snow storm, behave like this.

What did the polar vortex do?

A polar vortex is a large pocket of very powerful circular air/wind in the northern polar region during the winter season. And it has moved southwards, freezing the US and Canada. What caused the polar vortex to move? According to meteorologist Brett Anderson, the polar vortex moves around sometimes but now it has been so fierce because a powerful high pressure system from the eastern Pacific pushed to the North Pole, disturbing the vortex and it naturally blew over south, Canada and the US. When pressure from the Pacific weakens, the polar vortex will retreat.

A polar vortex, the cyclonic wind, is there at both of a planet's geographical poles. In earth's northern hemisphere, the air is circulating counter-clockwise. According to some experts, the phenomenon of sudden stratospheric warming appears during the winter in the northern hemisphere. What has happened is this cold air whirling around the Arctic, blasted southwards more than usual.

And this, a section of meteorologists attribute to global warming. They say as the vortex weakens, snow and chill come to the middle latitudes. The Arctic is warming, they claim.

“If you’ve been hearing that extreme cold spells, like the one we’re having in the United States now, disproves global warming, don’t believe it,” President Barack Obama’s science adviser, Dr. John Holdren, says in a video posted to the official White House website named 'The polar vortex explained in two minutes'. “A growing body of evidence suggests that the extreme cold being experienced by much of the United States as we speak is a pattern that we can expect to see with increasing frequency as global warming continues,” he said.

Meanwhile, experts on the subject have joined an online discussion for the White House. They are: Jason Samenow, weather editor at Washington Post, Dr J Marshall Shepherd, president of the American Meteorological Society and Professor, University of Georgia, Jim Overland, Arctic researcher at the National Oceanic and Atmospheric Administration (NOAA), and others. Organising the 'We The Geeks Session', a White House release said, cold spell may become more frequent in a world that’s getting warmer because of greenhouse-gas pollution. (ALSO SEE: President Obama's Plan to Fight Climate Change)