An expanding polar vortex is expected to lower temperatures across the eastern half of the U.S., with the potential for record-breaking cold in January.

The polar vortex is an area of cold air that circulates around the Arctic. That area can shift and expand, bringing lower temperatures further south than usual. Modelling by the independent forecaster Atmospheric and Environmental Research shows the polar vortex expanding over the US in the first two weeks of the new year.