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The Fujita Scale was introduced in 1971 by Tetsuya Theodore Fujita of the University of Chicago who developed the scale together with Allen Pearson, then head of the National Severe Storms Forecast Center in the USA.
The scale was retrospectively applied to tornado reports from 1950 onwards and was widely adopted thereafter. It was superseded in 2007 by the Enhanced Fujita (EF) Scale in the United States.
The Fujita Scale is used to categorise a Tornado retrospectively depending on the level of damage, although each damage level is associated with a wind speed. The Enhanced Fujita Scale was formulated after further research suggested that wind speeds on the Fujita scale were greatly overestimated. However, the EF scale wind speeds remain as educated guesses.
The scale ranges from F0, assigned to Tornadoes which cause only "light damage", through to F5, which is assigned to Tornadoes causing "incredible damage".
Tornadoes of F5 intensity are more common in the mid-western states of the USA and in Bangladesh than in Europe, but, even there, severe Tornadoes have caused great loss of life: On 9th June 1984, Tornadoes of F5, F4, and F3 intensity, caused hundreds of deaths and considerable damage across a wide area north of Moscow.