Simon King explains the weather to Ayshah Tull
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What causes a polar vortex?

6 January 2014 Last updated at 15:07 GMT

Parts of America are preparing for potentially record-breaking low temperatures, caused by an icy blast of air known as a polar vortex.

A winter storm has already covered north-eastern states and parts of Canada with snow.

Weather expert Simon King told Newsround how a polar vortex is formed - and how it's affecting the weather in the UK.