A severe winter storm is hitting a large part of the US, affecting more than 200 million people. Heavy snow and freezing temperatures are expected from Colorado to West Virginia, New York City, and Boston. The National Weather Service warns some areas could see more than a foot of snow. Over the weekend, more than 10,000 US flights were cancelled because of the bad weather. In Oklahoma, snow ploughs are working hard to clear roads and airport runways amid fierce blizzards. Video footage shows the tough battle against the heavy snow to keep transportation running.