The tornado that killed 18 people, including 4 storm chasers, west of Oklahoma City Friday was wider than any tornado ever observed or surveyed according to the National Weather Service and leading tornado researcher, Howard Bluestein. The massive El Reno, Okla. twister reached an unthinkable maximum width of 2.6 miles. “This is the biggest ever,” Bluestein said. The El Reno tornado of May 31, 2013 is officially the widest known tornado in the U.S. Rated EF-5. ow.ly/i/2hfDG #okwx #txwx.