After setting record-low temperatures in dozens of major U.S. cities, the painfully cold “polar vortex” is leaving the States and moving north to Canada. Sub-zero temperatures slowed life to a crawl in places like Minneapolis, which spent 62 straight hours below zero, and Chicago, which spent 37 straight hours below. The “polar vortex” is a cyclone of high winds from the North Pole, brought south by changes in the jet stream.
