This NOAA satellite image taken Sunday, January 05, 2014 at 01:45 PM EST shows widespread clouds affecting the eastern United States as moisture was surging north ahead of developing low pressure in the Ohio Valley
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US weather: BBC explains why it is so cold

6 January 2014 Last updated at 03:06 GMT

Temperatures in parts of the United States could drop to record lows of -30C (-22F) as a result of a "polar vortex" of cold, dense air.

John Hammond from the BBC Weather Centre explains what causes the unusual phenomenon.