According to the NOAA’s National Weather Service Storm Prediction Center website (http://www.spc.noaa.gov), The Fujita Scale, designed to measure the intensity and area of a tornado, was introduced in 1971. Since then, the F-Scale has become a part of the record of tornados across the United States. The Enhanced Fujita Scale, which addresses additional factors in measuring tornadoes, was introduced in the 1990s, and since that time, scientists have continued to study and revise the measuring of tornadoes.
 
Click here to access the Enhanced F Scale for Tornado Damage provided by the Storm Prediction Center, NOAA/National Weather Service.