A long-awaited blast of cold air, courtesy of the polar vortex, will overtake much of the US, but the forecast says the low temperatures won't last.

This cold blast could be relatively short-lived, with a return to more typical wintry temperatures by later in December.

A long-awaited blast of cold air, courtesy of the polar vortex, will overtake much of the US, but the forecast says the low temperatures won't last.