The
Fujita scale (
F-Scale), or
FujitaPearson scale, is a scale for rating
tornado intensity, based primarily on the damage tornadoes inflict on human-built structures and vegetation. The official Fujita scale category is determined by
meteorologists and
engineers after a ground or aerial damage survey, or both; and depending on the circumstances, ground-swirl patterns (
cycloidal marks),
radar tracking,
eyewitness testimonies, media reports and damage imagery, as well as
photogrammetry or
videogrammetry if motion picture recording is available.
The scale was introduced in 1971 by
Tetsuya Fujita of the
University of Chicago, in collaboration with
Allen Pearson, head of the
National Severe Storms Forecast Center (currently the
Storm Prediction Center). The scale was updated in 1973, taking into account path length and width. In the United States, starting in 1973, tornadoes were rated soon after occurrence. The Fujita scale was applied retroactively to tornadoes reported between 1950 and 1972 in the
National Oceanic and Atmospheric Administration (NOAA) National Tornado Database. Fujita rated tornadoes from 19161992[
clarification needed] and
Tom Grazulis of The Tornado Project retroactively rated all known significant tornadoes (F2F5 or causing a fatality) in the U.S. back to 1880.
In 2007, the Fujita scale was updated, and the
Enhanced Fujita Scale was introduced in the United States. The new scale more accurately matches wind speeds to the severity of damage caused by the tornado.
Though each damage level is associated with a wind speed, the Fujita scale is effectively a damage scale, and the wind speeds associated with the damage listed aren't rigorously verified. The Enhanced Fujita Scale was formulated due to research which suggested that the wind speeds required to inflict damage by intense tornadoes on the Fujita scale are greatly overestimated. A process of
expert elicitation with top engineers and meteorologists resulted in the EF scale wind speeds, however, these are biased to United States construction practices. The EF scale also improved damage parameter descriptions.
