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The F-Scale: Wind Speed and Damage

It is not easy to measure wind speed in a tornado. This is because a tornado usually destroys local measuring equipment, and also because tornadoes only exist for a short time at random places and they are gone before meteorologists can study them.

Wind speed is usually measured by a device called an anemometer, which has cups that spin around a vertical axis in the wind (the Beaufort wind scale rates, on a scale of 1 to 12, how strong the wind is). Severe tornadoes, however, can destroy these relatively fragile devices. There are other methods of measuring wind speed (including Doppler radar), but measuring the wind during a tornado is not easily done because tornadoes exist for such a short time. Meteorologists (weather scientists) may not even know about a tornado until after it has dissipated, since tornadoes usually only last for a few minutes and travel for a relatively short distance.

Before 1971, tornadoes were not ranked at all. In 1971, Dr. Theodore Fujita developed a method for categorizing tornadoes by looking at how much damage they cause and using this to estimate the wind speed. This system is called the F-Scale or Fujita Scale; it classifies tornadoes by their estimated wind speed, which is determined by looking at how strong the wind must have been to cause the resulting damage.

Tornadoes are classified into five categories, F-0 through F-5. F-0 tornadoes are the mildest. F-5 tornadoes are the most dangerous (and the rarest).

• F-0 40-72 mph, Light damage, chimney damage, tree branches broken
• F-1 73-112 mph, Moderate damage, mobile homes pushed off foundation or flipped over
• F-2 113-157 mph, Considerable damage, mobile homes demolished, trees uprooted
• F-3 158-205 mph, Severe damage, roofs and walls torn down, trains overturned, cars thrown around
• F-4 207-260 mph, Devastating damage, well-constructed walls leveled
• F-5 261-318 mph, Violent damage, homes lifted off foundation and carried considerable distances, autos thrown as far as 100 meters.
In 2006, the National Weather Service developed the Enhanced Fujita scale, with 28 different damage indicators.

Dr. Tetsuya Theodore Fujita
Dr. Tetsuya Theodore (Ted) Fujita (Oct. 23, 1920 - Nov. 19, 1998) was a pioneering meteorologist who revolutionized the study of severe storms. Dr. Fujita was the first person to realize that there are multiple vortex tornadoes, downbursts and microbursts. In 1971, Dr. Fujita developed the scale used for measuring wind speed, linking damage to estimated wind speed. This scale is called the Fujita-scale or the F-scale.

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