Tuesday, May 21st, 2013 — The tornado that slammed into the Oklahoma City suburb of Moore on Monday, killing more than 50 people with winds up to 200 miles per hour, was given a preliminary ranking of EF4, the second most powerful category on the Enhanced Fujita Scale. The Enhanced Fujita scale is an updated version of an earlier chart to measure the ferocity of tornadoes published in 1971 by a University of Chicago professor.