Tens of millions of people across North America are bracing for what could be the coldest air in a generation. A polar vortex is sweeping in from the Arctic and temperatures in some areas have already dropped as low as -46C.

North America braces for 'coldest air in a generation'

Tens of millions of people across North America are bracing for what could be the coldest air in a generation. A polar vortex is sweeping in from the Arctic and temperatures in some areas have already dropped as low as -46C.