Tornado classifications have evolved since the original Fujita (F scale) was developed in 1971. Under the original F scale, an F5 rating was given as follows: “Whole frame houses tossed off ...

May 20, 2013, marks the last time the United States was hit by the worst type of tornado. On that date ... right now than it was to attain an F5 rating on the legacy Fujita scale," Lyza said.