NEW : Fast-moving cold front knifes through southeastern U.S. , into U.S. . iReport : Show CNN how how the cold is affecting you . NEW : sub-zero deaths nationwide blamed on cold weather 112 years . NEW : Warmer air gradually will move eastward , with Key West the last to see relief . Key West , Florida , southernmost point in continental U.S. , has coldest day in this week .
NEW : Fast-moving cold front knifes through southeastern U.S. , into U.S. . NEW : sub-zero deaths nationwide blamed on cold weather 112 years . NEW : Warmer air gradually will move eastward , with Key West the last to see relief . Key West , Florida , southernmost point in continental U.S. , has coldest day in this week .