Polar Vortex

Polar Vortex: An area of low pressure in the upper atmosphere near both of the Earth’s geographical poles. In the winter of 2014, the regular polar vortex experienced a breakdown and a large part of the vortex was forced southward. Eventually the cold air in Canada and the mild temperatures in the United States merged which led to extreme wind chills and record cold temperatures in the central, southern and eastern parts of the United States.

Source: Wikipedia, Weather Underground