Denver International Airport announced at 12:18 p.m. on Wednesday that the airport is closed until further notice. "Weather and visibility are such that it is not safe for aircraft to arrive or depart at this time," airport officials tweeted. Airport officials said that passengers should not plan on coming to the airport until further notice and those at the airport should stay in place because Pena Blvd. is impassable. United Airlines canceled all remaining flights in and out of the airport .. Soutwest Airlines also canceled all remaining flights, ... Up to 12 inches of snow could fall at the...