Why is it so cold? Split in polar vortex brings historic deep freeze to US

The US is currently experiencing historically cold weather, with Chicago dropping to a low of around -23F (-30C) on Wednesday – but what is the cause of this extreme drop in temperature? A split in the polar vortex has been identified as the cause of the bitter cold that continued to sweep parts of the country on Thursday. The polar vortex is a mass of cold air that usually stays bottled up in the Arctic.

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