Weather researchers are warning that a polar vortex could hit North America over the festive period, bringing heavy snow and freezing conditions to the U.S. and to Canada.
According to the Washington Post, experts believe there is a chance that the weather phenomenon -- which usually sits over the Arctic Circle -- could move south in the coming weeks. Such a weather pattern could presage a return of the extreme conditions that hit much of the United States in February and March of this year.
It was Judah Cohen, a climate expert at Atmospheric and Environmental Research, who first warned of the risk in a Twitter post. He said, "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."
The polar vortex is like a river of wind which usually circles the North Pole. While it remains stable, weather in the northern hemisphere remains relatively normal. But if the vortex is disrupted, it can bring extreme weather conditions.
Earlier this year, temperatures then dropped well below zero in the northern states -- with some places like North Dakota and Minnesota dropping below minus 30 degrees Celsius, and snow blanketing much of the country. Such conditions always cause widespread disruption, and can be dangerous for elderly or vulnerable individuals.