The polar vortex of ultra-cold air usually spins around the North Pole, but it sometimes plunges south into the U.S., Europe and Asia. Studies show that a fast-warming Arctic is partly to blame for ...

The storm moved from the Rockies through the Central Plains, Ohio Valley and mid-Atlantic before exiting the U.S. Data from ...

Frigid air that normally stays trapped in the Arctic has escaped, plunging deep into the United States for an extended visit ...