http://www.noaa.gov/features/02_monitoring/warmarctic.html

“When the Polar Vortex — a ring of winds circling the Arctic —
breaks down, this allows cold air to spill south, affecting the eastern United
States and other regions,” says Dr. Overland. “This can result in a
warmer-than-average Arctic region and colder temperatures that may include
severe winter weather events on the North American and European continents.”