Airlines are cancelling thousands of flights into and out of East Coast airports as a major snowstorm packing up to three feet of snow barrels down on the region. Almost 1,900 flights scheduled for Monday have been cancelled, according to the flight tracking site FlightAware. Nearly 1,800 additional flights have been scrapped for Tuesday. Most major airlines are allowing customers whose flights are canceled in the next few days to book new flights without paying a penalty. Customers ticketed on flights to dozens of Eastern airports are generally eligible for the allowance, though specific terms vary by airline. The National Weather Service predicts 2 to 3 feet of snow for a 250-mile stretch of the Northeast, including the New York and Boston areas. Philadelphia should get 14 to 18 inches.