Fujita scale

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Fujita Scale
F0	F1	F2	F3	F4	F5

The Fujita scale (F-Scale), or Fujita-Pearson scale, rates a tornado's intensity by the damage it inflicts on human-built structures and sometimes on vegetation. The rating is of the most severe damage to any well-built frame home or comparable level of damage from engineering analysis of other damage. 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, eyewitness testimonies, media reports and damage imagery, and sometimes photogrammetry/videogrammetry.

Educated guesses at wind speed ranges were made based on the damage seen, but the original numbers have since been found to be higher than the actual wind speeds required to incur the damage described at each category. The error manifests itself to an increasing degree as the category increases, especially in the range of F3 through F5. The wind speeds listed should not be taken literally—the National Oceanic and Atmospheric Administration notes that …precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place—even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown. ^[1]

Beginning on February 1, 2007, the Fujita scale will be updated to the Enhanced F Scale (EF Scale) for operational use in the United States. The Enhanced F Scale accounts for different degrees of damage that occur with different types of structures, as well as damage to things other than structures.

The scale 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.

1 Current Fujita scale
- 1.1 Derivation
- 1.2 Parameters
2 The Enhanced F-Scale (EF Scale)
- 2.1 Parameters
- 2.2 Differences in the new scale
3 See also
4 References
5 External links

[edit] Current Fujita scale

[edit] Derivation

The gap between F0 and F1 corresponds to the eleventh and twelfth levels of the Beaufort scale, "violent storm" and "hurricane" respectively. Theoretically, the wind speeds for F11 and F12 correspond to Mach numbers 0.9 and 1.0 respectively. This provides a smooth relationship between the three scales. From these wind speed numbers, qualitative descriptions of damage were made for each category of the Fujita scale, and then these descriptions are used to classify tornadoes.^[2]

The diagram on the left illustrates the relationship between the Beaufort, Fujita, and Mach number scales.

[edit] Parameters

The six categories are, in order of increasing intensity (F6 is not in use):

Category F0	Wind speed	Less than 73 mph	Less than 116 km/h	Relative frequency	38.9%
Category F0	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 mph	116–180 km/h	Relative frequency	35.6%
Category F1	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 mph	181–250 km/h	Relative frequency	19.4%
Category F2	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 mph	251–330 km/h	Relative frequency	4.9%
Category F3	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 mph	331–415 km/h	Relative frequency	1.1%
Category F4	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 mph	416–510 km/h	Relative frequency	Less than 0.1%
Category F5	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 m (100 yd); trees debarked; steel reinforced concrete structures badly damaged; incredible phenomena will occur.
Category F6	Wind speed	319–379 mph	511–609 km/h	Relative frequency	never observed
Category F6	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. The F6 level, while present in Dr. Ted Fujita's original wind scale, is not an official damage level and is not used to rate tornadoes. There is, by definition, no such thing as an 'F6' tornado.^[1]

(*) This table presents the relative frequency of tornadoes in the United States. Frequencies of strong tornadoes (F2 or greater) are significantly less elsewhere in the world. Canada, Bangladesh and adjacent areas of eastern India also have frequent severe tornadoes, however statistics in these countries have not been studied thoroughly.

[edit] The Enhanced F-Scale (EF Scale)

The list below is the Enhanced Fujita Tornado Scale (EF Scale) to take effect February 1, 2007. The scale was revised to reflect better examinations of tornado damage surveys so as to align wind speeds more closely with associated storm damage. The new scale was publicly unveiled at a conference by the American Meteorological Society in Atlanta on February 2, 2006.

The new scale has to do with how most structures are designed. The wind speeds on the original scale were deemed by meteorologists as being too large and engineering studies have shown that slower winds can cause the same damage as that of winds of 300 mph. The new scale lists an EF-5 as a tornado with winds at or above 200 mph (324 km/h) – which corresponds to the wind speeds of F3 or F4 in the original Fujita scale. None of the tornadoes recorded on or before January 31, 2007 will be re-categorized.

Essentially, there is no functional difference in how tornadoes are rated. The old ratings and new ratings are cleanly connected with a linear formula. The only differences are adjusted wind speeds, measurements of which weren't used in previous ratings, and refined damage descriptors.

[edit] Parameters

The six categories for the EF Scale are, in order of increasing intensity:

Category EF0	Wind speed	65–85 mph	105–137 km/h
Category EF0	Potential damage	EF0 damage example Light damage. Peels surface off roofs; some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; mobile homes pushed off foundations or overturned; sign boards damaged.
Category EF1	Wind speed	86–110 mph	138–179 km/h
Category EF1	Potential damage	EF1 damage example Moderate damage. Roofs torn off frame houses; windows and glass doors broken; moving autos blown off roads; mobile homes demolished; boxcars overturned.
Category EF2	Wind speed	111–135 mph	180–217 km/h
Category EF2	Potential damage	EF2 damage example Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
Category EF3	Wind speed	136–165 mph	218–266 km/h
Category EF3	Potential damage	EF3 damage example Severe damage. Some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance.
Category EF4	Wind speed	166–200 mph	267–324 km/h
Category EF4	Potential damage	EF4 damage example Devastating damage. Well-constructed houses and whole frame houses completely leveled; structures with weak foundations blown away some distance; trees debarked; cars thrown and small missiles generated.
Category EF5	Wind speed	>200 mph	>324 km/h
Category EF5	Potential damage	EF5 damage example Incredible damage. Strong frame houses leveled off foundations and swept away; with strongest winds, brick houses completely wiped off foundations; automobile-sized missiles fly through the air in excess of 100 m (109 yd); cars thrown and large missiles generated; incredible phenomena will occur.

[edit] Differences in the new scale

Twenty-eight Damage Indicators (DI) will be used in the new system with Degrees of Damage (DOD) to determine wind estimates. Different buildings depending on building material will have their own DIs and DODs.

Since the new system will still use actual tornado damage to estimate the storm's wind speed, the National Weather Service states that the new scale will likely not lead to an increase in a number of tornadoes classified as EF5 (the lower wind speed ranges have been adjusted as better estimates of what is needed to incur the damage). The upper bound of the wind speed range for EF5 is open — in other words, there is no maximum wind speed designated.