Disasters like these are getting worse. From 1954 to 1963, the average outbreak—a sequence of six or more F1 or greater tornadoes that begin within six hours of each other—contained 11.4 storms. Half a century later, that number had risen to 16.1. Researchers are working to determine which weather and climate factors drive the clobbering hordes, but they can't be certain quite yet. What we do know is that it's increasingly likely we'll have a day like the one mapped out above again.