What is a Fujita Scale?

The Fujita Scale (F-Scale), also known as the Fujita-Pearson Scale, is a scale used for assigning an intensity rating to tornadoes. The rating assigned to a given tornado is based on the amount of damage the tornado causes to vegetation, landscape, and artificial structures. In 1971, Tetsuya Theodore "Ted" Fujita of the University of Chicago, in association with Allen Pearson, first introduced the scale. At the time, Pearson was the head of the National Severe Storms Forecast Center, the forerunner of the Storm Prediction Center, in Kansas City, Missouri.

After a tornado, engineers and meteorologists assign an official Fujita rating to the cyclone following visual surveys of the area. These surveys are performed by land and/or ground, depending on the circumstances and accessibility. Ground-swirl patterns called "cycloidal marks" may also be used to determine the tornado's intensity. Eyewitness accounts, media reports and recordings, and radio tracking may also be used in order to accurately rate the tornado.

Ratings using the Fujita-Pearson scale were retroactively applied to tornadoes reported from 1950 forward. These rating assignments were entered into the National Oceanic and Atmospheric Administration (NOAA) National Tornado Database. Ratings were also applied to numerous strong, infamous tornadoes that occurred prior to 1950.

The Enhanced Fujita Scale officially replaced the original Fujita Scale in the United States in 2007, using ratings of EF0 through EF5 rather than F0 through F5. In brief, F0/EF0 indicates light damage; F1/EF1 indicates moderate damage; F2/EF2 indicates considerable damage; F3/EF3 indicates severe damage; F4/EF4 indicates devastating damage, and F5/EF5 indicates incredible damage. Neither the Fujita Scale nor the Enhanced Fujita Scale are wind speed or wind classification scales, but damage scales, even though the levels within each correlate to a range of wind speeds. The Enhanced Fujita Scale came into existence as a result of research that suggested wind speeds for stronger tornadoes on the original Fujita Scale were overestimated to a great degree.

The Enhanced Fujita Scale takes construction quality into consideration. It also standardizes different types of structures. Other than that, the two systems are essentially the same. According to the National Weather Service (NWS) in the United States, there are no plans to re-evaluate past tornadoes using the Enhanced Fujita Scale, and it's unlikely that a higher percentage of future cyclones will receive a level "5" rating because of the switch.

The Enhanced Fujita Scale, like its predecessor that is still used in parts of the world other than the United States, is still a damage scale that employs estimates for wind speeds. The new scale was used in the United States for the first time a year after its February 2006 announcement, and was applied to a rash of tornadoes that ripped through central Florida. The strongest rating on the Enhanced Fujita Scale, EF5, was assigned for the first time to the devastating tornado that flattened the small town of Greensburg, Kansas, in May 2007.