A powerful cold front is expected to rip through the Northeast and Midwest this week, with extreme temperatures reaching as low as -45 degrees as the US braces for the coldest air chill in three years. More than 15 million people are under wind chill advisories after temperatures plummeted to -25 to -45 degrees on Monday. The National Weather Service also warns that parts of northern New York and Massachusetts could see wind chills of between 35 and 40 below zero between 7pm Monday to 3pm on Tuesday that could cause 'frostbite on exposed skin in as little as 10...