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The TORRO tornado intensity scale (or T-Scale) is a scale measuring tornado intensity between T0 and T11. It was proposed by Terence Meaden of the Tornado and Storm Research Organisation (TORRO), a meteorological organisation in the United Kingdom, as an extension of the Beaufort scale.
The scale was tested from 1972 to 1975 and was made public at a meeting of the Royal Meteorological Society in 1975. The scale sets T0 as the equivalent of 8 on the Beaufort scale and is related to the Beaufort scale (B), up to 12 on the Beaufort scale, by the formula:
and conversely:
| Beaufort scale | B | 8 | 10 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 |
| TORRO scale | T | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
The Beaufort scale was first introduced in 1805, and in 1921 quantified. It expresses the wind speed as faster than v in the formula:
Most UK tornadoes are T6 or below with the strongest known UK tornado estimated as a T8 (the London tornado of 1091). For comparison, the strongest detected winds in a United States tornado (during the 1999 Oklahoma tornado outbreak) would be T11 using the following formulas:
where v is wind speed and T is TORRO intensity number. Wind speed is defined as a 3-second gust at 10 m AGL.
Alternatively, the T-Scale formula may be expressed as:
or
 | This section needs to be updated.(December 2023) |
TORRO claims it differs from the Fujita scale in that it is "purely" a wind speed scale, whereas the Fujita scale relies on damage for classification, but in practice, damage is utilised almost exclusively in both systems to infer intensity. That is because such a proxy for intensity is usually all that is available, although users of both scales would prefer direct, objective, quantitative measurements. The scale is primarily used in the United Kingdom whereas the Fujita scale has been the primary scale used in North America, continental Europe, and the rest of the world.
At the 2004 European Conference on Severe Storms, Dr. Meaden proposed a unification of the TORRO and Fujita scales as the Tornado Force or TF Scale. [1] In 2007 in the United States, the Enhanced Fujita Scale replaced the original Fujita Scale from 1971. [2] It made substantial improvements in standardizing damage descriptors through expanding and refining damage indicators and associated degrees of damage, as well as calibrated tornado wind speeds to better match the associated damage. [3] However, the EF Scale, having been designed based on construction practices in the United States, is not necessarily applicable across all regions. [4] [5] The EF-scale and variants thereof are officially used by the United States, Canada, [6] [7] France, [8] and Japan, [9] as well as unofficially in other countries, such as China. [10]
Unlike with the F scale, no analyses have been undertaken at all to establish the veracity and accuracy of the T scale damage descriptors. The scale was written in the early 1970s, and does not take into account changes such as the growth in weight of vehicles or the great reduction in numbers and change of type of railway locomotives,[ citation needed ] and was written in an environment where tornadoes of F2 or stronger are extremely rare, so little or no first-hand investigation of actual damage at the upper end of the scale was possible. The TORRO scale has more graduations than the F scale which makes it arguably more useful for tornadoes on the lower end of the scale[ citation needed ]; however, such accuracy and precision are not typically attainable in practice. Brooks and Doswell stated that "the problems associated with damage surveys and uncertainties associated with estimating wind speed from observed damage make highly precise assignments dubious". [11] In survey reports, Fujita ratings sometimes also have extra qualifications added ("minimal F2" or "upper-end F3 damage"), made by investigators who have experience of many similar tornadoes and relating to the fact that the F scale is a damage scale, not a wind speed scale.[ citation needed ]
Tornadoes are rated after they have passed and have been examined, not whilst in progress. In rating the intensity of a tornado, both direct measurements and inferences from empirical observations of the effects of a tornado are used. Few anemometers are struck by a tornado, and even fewer survive, so there are very few in-situ measurements. Therefore, almost all ratings are obtained from remote sensing techniques or as proxies from damage surveys. Weather radar is used when available, and sometimes photogrammetry or videogrammetry estimates wind speed by measuring tracers in the vortex. In most cases, aerial and ground damage surveys of structures and vegetation are utilised, sometimes with engineering analysis. Also sometimes available are ground swirl patterns (cycloidal marks) left in the wake of a tornado. If an on site analysis is not possible, either for retrospective ratings or when personnel cannot reach a site, photographs, videos, or descriptions of damage may be utilised.
The 12 categories for the TORRO scale are listed below, in order of increasing intensity. Although the wind speeds and photographic damage examples are updated, which are more or less still accurate.[ citation needed ] However, for the actual TORRO scale in practice, damage indicators (the type of structure which has been damaged) are predominantly used in determining the tornado intensity.
| Scale | Wind speed (Estimated) | Potential damage | Example of damage | ||
| mph | km/h | m/s | |||
| T0 | 39 - 54 | 61 - 86 | 17 - 24 | Light damage. Loose light litter raised from ground level in spirals. Tents, and marquees seriously disturbed; most exposed tiles slates on roofs dislodged. Twigs snapped; trail visible through crops. Paper and leaves lifted off the ground. | |
| T1 | 55 - 72 | 87 - 115 | 25 - 32 | Mild damage. Deckchairs, small plants, heavy litter becomes airborne; minor damage to sheds. More serious dislodging of tiles, slates, chimney pots. Wooden fences flattened. Slight damage to hedges and trees. | |
| T2 | 73 - 92 | 116 - 147 | 33 - 41 | Moderate damage. Heavy mobile homes displaced, light caravans blown over, garden sheds destroyed, garage roofs torn away, much damage to tiled roofs and chimney stacks. General damage to trees, some big branches twisted or snapped off, small trees uprooted. | |
| T3 | 93 - 114 | 148 - 184 | 42 - 51 | Strong damage. Mobile homes overturned / badly damaged; light caravans destroyed; garages and weak outbuildings destroyed; house roof timbers considerably exposed. Some of the bigger trees snapped or uprooted. | |
| T4 | 115 - 136 | 185 - 220 | 52 - 61 | Severe damage. Motor cars levitated. Mobile homes airborne / destroyed; sheds airborne for considerable distances; entire roofs removed from some houses; roof timbers of stronger brick or stone houses completely exposed; gable ends torn away. Numerous trees uprooted or snapped. | |
| T5 | 137 - 160 | 221 - 259 | 62 - 72 | Intense damage. Heavy motor vehicles levitated; more serious building damage than for T4, yet house walls usually remaining; the oldest, weakest buildings may collapse completely. (e.g. 2005 Birmingham tornado) | |
| T6 | 161 - 186 | 260 - 299 | 73 - 83 | Moderately - devastating damage. Strongly built houses lose entire roofs and perhaps also a wall; windows broken on skyscrapers, more of the less-strong buildings collapse. (e.g. 1913 United Kingdom tornado outbreak) | |
| T7 | 187 - 212 | 300 - 342 | 84 - 95 | Strongly - devastating damage. Wooden-frame houses wholly demolished; some walls of stone or brick houses beaten down or collapse; skyscrapers twisted; steel-framed warehouse-type constructions may buckle slightly. Locomotives thrown over. Noticeable debarking of trees by flying debris. (e.g. 2008 Poland tornado outbreak) | |
| T8 | 213 - 240 | 343 - 385 | 96 - 107 | Severely - devastating damage. Motor cars hurled great distances. Wooden-framed houses and their contents dispersed over long distances; stone or brick houses irreparably damaged; skyscrapers badly twisted and may show a visible lean to one side; shallowly anchored high rises may be toppled; other steel-framed buildings buckled. (e.g. 2021 South Moravia tornado) | |
| T9 | 241 - 269 | 386 - 432 | 108 - 120 | Intensely - devastating damage. Many steel-framed buildings badly damaged; skyscrapers toppled; locomotives or trains hurled some distances. Complete debarking of any standing tree-trunks. (e.g. 1984 Ivanovo tornado) | |
| T10 | 270 - 299 | 433 - 482 | 121 - 134 | Super damage. Entire frame houses and similar buildings lifted bodily or completely from foundations and carried a large distance to disintegrate. Steel-reinforced concrete buildings may be severely damaged or almost obliterated. | |
| T11 | >300 | >483 | >135 | Phenomenal damage. Strong framed, well built houses leveled off foundations and swept away. Mansions are completely swept, only their flooring or foundations remain, with no trace of debris. Steel-reinforced concrete structures are completely destroyed. Tall buildings collapse. Some cars, trucks and train cars can be thrown approximately 1 mile (1.6 kilometres). (e.g. 1997 Jarrell, Texas Tornado) | |
| T0 | T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 | T9 | T10 | T11 |
| Weak | Strong | Violent | |||||||||
The Fujita scale, or Fujita–Pearson scale, is a scale for rating tornado intensity, based primarily on the damage tornadoes inflict on human-built structures and vegetation. The official Fujita scale category is determined by meteorologists and engineers after a ground or aerial damage survey, or both; and depending on the circumstances, ground-swirl patterns, weather radar data, witness testimonies, media reports and damage imagery, as well as photogrammetry or videogrammetry if motion picture recording is available. The Fujita scale was replaced with the Enhanced Fujita scale (EF-Scale) in the United States in February 2007. In April 2013, Canada adopted the EF-Scale over the Fujita scale along with 31 "Specific Damage Indicators" used by Environment Canada (EC) in their ratings.
An extremely rare wintertime tornado outbreak affected the Midwestern United States on January 24, 1967. Of the 30 confirmed tornadoes, 13 occurred in Iowa, nine in Missouri, seven in Illinois, and one in Wisconsin. The outbreak produced, at the time, the northernmost tornado to hit the United States in winter, in Wisconsin, until January 7, 2008. The tornadoes formed ahead of a deep storm system in which several temperature records were broken. The deadliest and most damaging tornado of the outbreak struck Greater St. Louis at F4 intensity, killing three people and injuring 216.
The Enhanced Fujita scale rates tornado intensity based on the severity of the damage they cause. It is used in some countries, including the United States and France The EF scale is also unofficially used in other countries including China.
Tornado intensity is the measure of wind speeds and potential risk produced by a tornado. Intensity can be measured by in situ or remote sensing measurements, but since these are impractical for wide-scale use, intensity is usually inferred by proxies, such as damage. The Fujita scale, Enhanced Fujita scale, and the International Fujita scale rate tornadoes by the damage caused. In contrast to other major storms such as hurricanes and typhoons, such classifications are only assigned retroactively. Wind speed alone is not enough to determine the intensity of a tornado. An EF0 tornado may damage trees and peel some shingles off roofs, while an EF5 tornado can rip well-anchored homes off their foundations, leaving them bare— even deforming large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes. Doppler radar data, photogrammetry, and ground swirl patterns may also be analyzed to determine the intensity and assign a rating.
A violent severe weather outbreak struck the Southeast on April 4–5, 1977. A total of 22 tornadoes touched down with the strongest ones occurring in Mississippi, Alabama, and Georgia. The strongest was a catastrophic F5 tornado that struck the northern Birmingham, Alabama, suburbs during the afternoon of Monday, April 4. In addition to this tornado, several other tornadoes were reported from the same system in the Midwest, Alabama, Georgia, Mississippi and North Carolina. One tornado in Floyd County, Georgia, killed one person, and another fatality was reported east of Birmingham in St. Clair County. In the end, the entire outbreak directly caused 24 deaths and 158 injuries. The storm system also caused the crash of Southern Airways Flight 242, which killed 72 and injured 22.
On August 28, 1884, a tornado outbreak, including a family of least five strong tornadoes, affected portions of the Dakota Territory within present-day South Dakota. Among them was one of the first known tornadoes to have been photographed, an estimated F4 on the Fujita scale, that occurred near Howard and exhibited multiple vortices. Another violent tornado also occurred near Alexandria, and three other tornadoes were also reported. A sixth tornado also occurred in present-day Davison County. In all, the tornadoes killed at least seven people and injured at least two others. Contemporary records and survivors' recollections indicate that the storms were F3 or F4 intensity on the Fujita scale, but cannot currently be officially verified, as official records begin in 1950.
On January 11, 1898, a series of tornadoes affected the U.S. states of Arkansas and Missouri, as well as the Indian Territory, presently Oklahoma. At least five in all, these included the Fort Smith tornado, which struck the city of Fort Smith, Arkansas. Retroactively rated a violent (F4) tornado on the modern-day Fujita scale, it was part of a tornado family that formed 60 mi (97 km) to the southwest, and struck the city around midnight, killing 55 people and injuring 113. The twister nearly destroyed the newly constructed Fort Smith High School that had opened in fall 1897. Other tornadoes were reported that night in Arkansas and Missouri. The Fort Smith tornado is tied with one that struck Warren in 1949, also rated F4, for the deadliest tornado to strike Arkansas.
The March 1875 Southeast tornado outbreak was a deadly tornado outbreak that affected portions of the Southern United States from March 19–20, 1875. At least 19 tornadoes were recorded, including seven that were destructive enough to be rated F4 by Thomas P. Grazulis. The worst damage and most of the deaths occurred in Georgia. Most of the damage appears to have been the result of two tornado families that moved along parallel paths 12 to 15 mi apart through parts of Georgia and South Carolina. These families each consisted of numerous long-tracked, intense tornadoes. The deadliest tornado of the outbreak was an estimated F4 that killed 28–42 people in and near Sparta, Georgia, and Edgefield, South Carolina, on March 20. A separate F4 that followed a similar trajectory may have killed as many as 30. In all, this outbreak killed at least 96 people, injured at least 377, and caused at least $650,000 in losses.
On April 20 – 22, 1912, a large tornado outbreak affected portions of the High Plains, the Upper Midwest, and the Southern United States, including portions of what is now known as the Dallas–Fort Worth metroplex. The severe-weather event produced at least 32 tornadoes, at least nine—and possibly 10 or more—of which were violent tornadoes, all of which rated F4 on the Fujita scale. Powerful tornado activity was distributed from the Great Plains to South Carolina. The first day of the outbreak occurred on April 20 and produced numerous strong to violent tornadoes across parts of North Texas, Oklahoma, and Kansas. A second day of intense tornadoes occurred on April 21, with several strong to violent tornadoes across Illinois and Indiana. The final day, April 22, produced an F4 tornado in Georgia as well. The entire outbreak killed 56 people, and was followed days later by another intense tornado outbreak on April 27. That outbreak killed about 40 people, mostly in Oklahoma. Both outbreaks produced a combined total of nine F4 tornadoes in Oklahoma alone.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
A deadly tornado outbreak devastated parts of Louisiana and Tennessee on February 11–13, 1950. The outbreak covered about a day and a half and produced numerous tornadoes, mostly from East Texas to the lower Mississippi Valley, with activity concentrated in Texas and Louisiana. Most of the deaths occurred in Louisiana and Tennessee, where tornadoes killed 25 and 9 people, respectively. Several long-lived tornado families struck the Red River region of northwestern Louisiana, especially the Shreveport–Bossier City area. One of the tornadoes attained violent intensity, F4, on the Fujita scale and caused eight deaths, including six at the Shreveport Holding and Reconsignment Depot near Barksdale Air Force Base. It remains one of the top ten deadliest tornadoes on record in the state of Louisiana, in tenth place. Also in Louisiana, two other destructive tornadoes on parallel paths killed 16. Seven additional deaths occurred across the border in East Texas. Nine people died in a tornado in western Tennessee as well. In all, the entire outbreak killed at least 41 people and left 228 injured. Also, several long-tracked tornadoes recorded in the outbreak likely contained more, shorter-lived tornadoes.
On April 18–20, 1880, a tornado outbreak impacted the Midwestern United States, producing numerous strong tornadoes, killing at least 166 people, and injuring more than 516 others. The outbreak generated five violent tornadoes, including three long-tracked F4 tornadoes in Missouri that killed at least 144 people. Two of the tornadoes followed parallel paths and occurred simultaneously near Springfield, one of which devastated the town of Marshfield, causing 92 fatalities there. Other deadly, intense tornadoes occurred in the Great Lakes region and in Arkansas, including another F4 tornado that destroyed a third of El Paso, Arkansas, killing four or more people.
On Thursday, September 29, 1927, an outbreak of at least 15 significant tornadoes, including three F3 tornadoes, killed at least 82 people in the Central United States, particularly in Missouri and Illinois. The outbreak affected a broad expanse of the Midwestern and Southern United States, including Oklahoma, Missouri, Arkansas, Iowa, Illinois, and Indiana. The deadliest tornado was an estimated F3 which affected portions of Greater St. Louis, killing at least 79 people and injuring at least 550 others. The tornado narrowly missed Downtown St. Louis, striking north of the central business district before crossing the Mississippi River.
On October 3–4, 1964, Hurricane Hilda and its remnants generated a tornado outbreak over portions of the Southeastern United States. The outbreak, which yielded at least 12 confirmed tornadoes, killed 22 people and injured 175 others. Most of the casualties occurred as a result of a violent tornado that devastated the northern outskirts of Larose, Louisiana, becoming the deadliest hurricane-generated tornado on record since 1900 and one of only two violent tornadoes (F4+) recorded in the southern Gulf Coast region of Louisiana. The tornado was also one of only two F4s known to have been produced by a tropical cyclone, the other having occurred during Hurricane Carla on September 12, 1961.
The International Fujita scale rates the intensity of tornadoes and other wind events based on the severity of the damage they cause. It is used by the European Severe Storms Laboratory (ESSL) and various other organizations including Deutscher Wetterdienst (DWD) and State Meteorological Agency (AEMET). The scale is intended to be analogous to the Fujita and Enhanced Fujita scales, while being more applicable internationally by accounting for factors such as differences in building codes.
On May 2, 1942, a deadly tornado outbreak affected portions of the Central United States, particularly Northeastern Oklahoma and Southeast Kansas. In the latter areas the severe weather event produced at least four violent, long-tracked tornado families, retroactively assessed as having inflicted F4 damage, that varied in length from 55 to 88 mi. Altogether these claimed 29 lives and injured at least 158 people, featuring six known tornadoes, all rated F4. Besides these, the outbreak also yielded two other tornadoes, both deadly: a long-lived F3 family in Illinois that killed one person and an F2 in Missouri that killed one more. The entire outbreak killed 31 people and injured at least 172.
