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.
In rating the intensity of tornadoes, meteorologists and other experts study damage on the ground, along with wind speeds and other data, to rate twisters between EF0 (the weakest) and EF5 (the most intense).
The scale is as follows:
* An EF5 tornado, capable of causing incredible damage, is characterized by three-second wind gusts between 200 and 234 mph and can level strong frame houses off their foundations, according to the National Oceanic and Atmospheric Administration (NOAA). Automobile-sized missiles can fly through the air in excess of 109 yards, and trees can be stripped of their barked.