The holiday hangover is particularly bad for U.S. air carriers as severe weather disruptions have continued to lead to thousands of flights being canceled around the country. By Monday afternoon, nearly 3,000 flights into and out of the U.S. had already been canceled and almost 5,000 had been delayed. Southwest Airlines accounted for more than 2,300 of those cancellations — over half of its scheduled trips for the day, according to FlightAware. Social media posts from some of the country’s major airports, including San Francisco International Airport and Denver International Airport, show incr…