Laborers shovel the snow off of the sidewalk in the midtown neighborhood of Detroit, Michigan January 6, 2014. A blast of Arctic air gripped the vast middle of the United States on Monday, with the coldest temperatures in two decades threatening lives, forcing businesses and schools to close and canceling thousands of flights. The polar vortex, the coldest air in the Northern hemisphere that hovers over the polar region in winter but can be pushed south, was moving toward the East Coastwhere temperatures were expected to fall into Tuesday. REUTERS/Rebecca Cook (UNITED STATES – Tags: ENVIRONMENT TPX IMAGES OF THE DAY)
