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 increasing frequency of the polar vortex extending its grip.

But, today, it’s all about the cold. Temperatures plunged into the teens and single digits in some spots, and the snow-dusted winds are driving the wind chill below zero. The polar vortex, a swirling mass of Arctic air typically contained over the North Pole, has pushed south, driving bone-chilling temperatures into the eastern United States.