Severe winter storm puts much of US on high alert

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More than 70 million Americans are under winter weather alerts as a huge winter storm is forecast to bring the heaviest snowfall and coldest temperatures in over a decade.

Thirty states are under weather alerts in an area spanning 1,500 miles (2,400km) from Kansas to the East Coast, the National Weather Service (NWS) said.

A state of emergency has been declared in Kentucky, Virginia, Kansas, Arkansas and Missouri. Parts of the US unaccustomed to severe cold, including Mississippi, Texas and Florida, have been warned to expect treacherous conditions.

Forecasters say the extreme weather is being caused by the polar vortex, an area of cold air that circulates around the Arctic.