WeatherWhys for May 2,2014 from accuweather.com

In the early part of May 1999, an outbreak of severe weather slammed the southern Plains and South. The strongest tornado, ranked F5, of this outbreak tore through the suburbs of Oklahoma City on May 3 and killed 36 people. This was the last F5 tornado to strike the United States. Tornadoes of this magnitude remained absent from the United States until May 4, 2007, when a tornado slammed Greensburg, Kansas. That twister was ranked as the first EF5 tornado under the new Enhanced Fujita scale of tornado intensity.