The US is being hit by the coldest freeze in years. Record-breaking cold and snow are expected as forecasters warn of life-threatening conditions and wind chill as low as 60 degrees below zero. A whirlpool of freezing, dense air known as a "polar vortex" has pummelled parts of the US with potentially record low temperatures and high snowfall. More than a foot of snow has been dumped on a large part of the Midwest, forcing officials to close schools in Chicago, St Louis and Milwaukee on Monday. Temperatures as low as -35C (-31F) are forecast for Fargo, North Dakota, while Madison, Wisconsin, will experience -29C (-21F) and even Chicago and Minneapolis could drop to -27C (-15F).