Tornadoes are formed when the cumulonimbus bodies of warm and cold air meet.
The contrasts in temperature cause the severe weather in twisting large cloud masses slowly on itself.
Is created inside the cloud of upward movements of air that can reach impressive speeds.
The Fujita scale is used to estimate the intensity of a tornado. The Fujita scale, or Fujita-Pearson scale, is a scale that ranks tornadoes by severity, depending on the damage they cause. The Fujita Scale was created in 1971 by the American researcher Tetsuya Theodore Fujita, meteorologist in collaboration with Allan Pearson, the Storm Prediction Center (forecast severe thunderstorms) in the United States. It was immediately adopted by the scientific community and weather.
- The force F0 is light winds from 60 to 120 km/h. The damage observed are broken branches, the deformation of signs, television antennas twisted...
- The force F1 is moderate winds from 120 to 180 km/h. The damage observed are torn tiles, trailers overturned,...
- The force F2 is strong winds ranging from 180 to 250 km/h. The damage is observed, trees and roofs torn off,... | | - The force F3 is winds from 250 to 330 km/h. The damage is observed, walls and roofs of buildings into the air, forests cut down.
- The force F4 corresponds to wind speeds of 330 to 420 km/h. The damage observed is, buildings without foundations and vehicles overturned.
- The F5 is extreme winds ranging from 420 to 510 km/h. The damage is observed, buildings razed, trains moved,...
The Fujita Scale does not reflect the quality of construction of structures damaged.
The fact that foundations were swept from office a class category F5 tornado.
Many studies have shown that the Fujita scale overestimated wind speeds in categories F3, F4 and F5.
The winds of a hypothetical tornado F12 reach the sound barrier.
For these reasons a new improved version was created by the U.S.
National Weather Service in 2006 and is now based on 28 indicators of damage, taking into account the type of building or structure. | | 
* More than 1 000 tornadoes develop each year in the United States, twenty reached levels 4 or 5 of the Fujita scale. |
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