Weather researchers say that a polar vortex could hit the United States and Canada with extremely frigid temperatures either by the end of this month or sometime in January.

Judah Cohen, who is a climate expert at Atmospheric and Environmental Research, said that the latest studies indicate there is a chance Arctic air could push southward and blanket much of the Northern Hemisphere in the coming weeks.

It all depends on the polar vortex, the patch of air 60,000 feet above the Earth’s Arctic surface, according to The Washington Post.

If the vortex stays stable, the winter will be quite ordinary, with its usual cold spells, snow storms, and thaws.

But if the vortex is disrupted, it would mean especially frigid temperatures similar to those which covered the United States in February and March.

Cohen tweeted: 'Confidence is growing in a significant polar vortex disruption in the coming weeks.

'This could be the single most important determinant of the weather this winter across the Northern Hemisphere.'

There is disagreement over the projections of a possible disruption in the vortex.

While American climate experts say it could happen later this month, European experts are predicting that January will be when it is felt.

The findings about a possible polar vortex contradict predictions by U.S. meteorologists who said in October that this coming winter will be warmer and milder than usual.

The National Weather Service predicted a warmer than normal winter for the northern and western three-quarters of the nation - thanks to a weak El Niño brewing.

The greatest chance for warmer than normal winter weather is in Alaska, the Pacific Northwest, Montana, northern Wyoming and western North Dakota.

No place in the United States is expected to be colder than normal, said Mike Halpert, deputy director of the government's Climate Prediction Center.

The Southeast, Ohio Valley and mid-Atlantic can go any which way on temperature, Halpert said.

Overall the winter looks a lot like the last few, Halpert said.

'The country as a whole has been quite mild since 2014-2105,' Halpert said.

THE NOAA WINTER FORECAST

Temperature:

Precipitation

Drought