Fujita scale

The Fujita scale, or Fujita-Pearson scale, rates a tornado's intensity by the damage it inflicts on human-built structures. Wind speed ranges were approximated to what was thought would cause the damage largely as educated guesses and have been found to be higher than the actual wind speeds required to incur the damage at each respective category (to an increasing degree as the category increases). It was introduced in 1971 by Tetsuya "Ted" Fujita of the University of Chicago who developed the scale together with Allen Pearson (path length and width additions in 1973), head of the National Severe Storms Forecast Center (predecessor to the Storm Prediction Center) in Kansas City, Missouri.

Fujita scale ratings are issued after a tornado has passed through an area, not while it is on the ground. The official Fujita scale category is determined after meteorologists (and engineers) examine damage, ground-swirl patterns, radar tracking, eye-witness testimonies, media reports and damage imagery, and sometimes photogrammetry / videogrammetry. A tornado will be assigned the rating of the most severe damage to any well-built frame home or comparable level of damage from engineering analysis of other damage.

Fujita Scale Parameters

The first six categories are, in order of increasing intensity :

Category F0	Wind speed	<73 mi/h	<115 km/h	Relative frequency	82%
	Potential damage	F0 damage example Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.
Category F1	Wind speed	73–112 mi/h	116–180 km/h	Relative frequency	11%
	Potential damage	F1 damage example Moderate damage. The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.
Category F2	Wind speed	113–157 mi/h	181–250 km/h	Relative frequency	4%
	Potential damage	F2 damage example Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated.
Category F3	Wind speed	158–206 mi/h	251–330 km/h	Relative frequency	1.8%
	Potential damage	F3 damage example Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
Category F4	Wind speed	207–260 mi/h	331–415 km/h	Relative frequency	0.9%
	Potential damage	F4 damage example Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.
Category F5	Wind speed	261–318 mi/h	416–510 km/h	Relative frequency	0.3%
	Potential damage	F5 damage example Incredible damage. Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters (109 yd); trees debarked; steel re-inforced concrete structures badly damaged; incredible phenomena will occur.

(*) Relative frequency is of tornadoes in the United States. Frequencies of strong tornadoes are significantly less anywhere else in the world save Canada, Bangladesh and adjacent areas of eastern India. Also, due to many tornadoes never inflicting damage, the F0 numbers are somewhat inflated, compared to what damage some of the tornadoes are capable of producing.

See also

• Beaufort scale
• TORRO scale
• Saffir-Simpson Hurricane Scale
• List of tornadoes and tornado outbreaks

External links

• The Fujita Scale of Tornado Intensity (Tornado Project)
• Fujita Tornado Damage Scale (SPC/NOAA)
• The Fujita Tornado Scale (NCDC/NOAA)
• Fujita Scale Enhancement Project (Wind Science and Engineering Research Center)

Category F6 Wind speed 319–379 mi/h 511–609 km/h Relative frequency <0.001% Potential damage Inconceivable damage. These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess 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.