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Fujita Tornado Scale

The Fujita Tornado Intensity Scale is a standard six-point scale used for rating the intensity of a tornado or other severe wind inferring its wind force from the type and extent of the damage it caused after it has passed over a man-made structure. It also measures both the path lenght and the path width.

The maximum wind speed is estimated and thus not comparable with direct measurements by Doppler radar. Class F5 tornadoes are rare. The scale was introduced in 1971 by Tetsuya Theodore Fujita and Allen Pearson and is also known as the Fujita-Pearson Scale.

The Fujita Scale may not be a perfect system for linking damage to wind speed, but it was simple to use in daily practice and it is widely accepted today.

picture However, one key point to remember is that the size of a tornado is not necessarily an indication of its intensity. Large tornadoes can be weak, small tornadoes van be violent. The Fujita scale is based on damage, not the appearance of the funnel. The Fujita scale is very subjective, and varies according to how experienced the surveyor is. The official rating is usually set by the national weather services.

Media hype and inexperience with tornado damage plays a big part in exaggerated F-Scale claims seen on television or in the papers.

The Fujita Tornado Damage Scale
light - some damage to chimneys; branches broken off trees, shallow-rooted trees uprooted, sign boards damaged
moderate - roof surfaces peeled off; mobile homes pushed foundations or overturned; moving autos pushed off road.
considerable - roofs torn from houses; mobile homes demolished; box cars pushed over; large trees uprooted; light objects become projectiles
severe - roofs and some walls torn from houses; trains overturned; most trees in forested area uprooted; heavy cars lifted and thrown
devastating - well-constructed houses leveled; structures with weak foundation blown some distance; cars thrown; large missiles generated
incredible - frame houses lifted off foundations, carried large distances, disintegrated; large bodies/missiles airborne; trees debarked

There is another innofficial Fujita force. F6 - inconceivable damage with estimated winds greater than 320 mph. These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the havoc produced by F4 and F5 wind that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever achieved, evidence for it might only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies

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