Fujita scale#Rating classifications

The scale was introduced in 1971 by Ted Fujita of the University of Chicago, in collaboration with Allen Pearson, head of the National Severe Storms Forecast Center/NSSFC (currently the Storm Prediction Center/SPC). The scale was updated in 1973, taking into account path length and width. In the United States, starting in the late 1970s,{{Cite journal |last1=Edwards |first1=Roger |last2=LaDue |first2=James G. |last3=Ferree |first3=John T. |last4=Scharfenberg |first4=Kevin |last5=Maier |first5=Chris |last6=Coulbourne |first6=William L. |date=2013-05-01 |title=Tornado Intensity Estimation: Past, Present, and Future |url=https://www.spc.noaa.gov/publications/edwards/ef-scale.pdf |journal=Bulletin of the American Meteorological Society |language=en |volume=94 |issue=5 |pages=641–653 |doi=10.1175/BAMS-D-11-00006.1 |bibcode=2013BAMS...94..641E |s2cid=7842905 |issn=1520-0477}} tornadoes were rated soon after occurrence. The Fujita scale was applied retroactively to tornadoes reported between 1950 and the adoption of the scale in the National Oceanic and Atmospheric Administration (NOAA) National Tornado Database. Fujita rated tornadoes from 1916 to 1992{{cite journal|title=American Meteorological Society |journal=Bulletin of the American Meteorological Society |volume=82 |pages=63–72 |doi=10.1175/1520-0477(2001)000<0063:TTFHCT>2.3.CO;2 |year = 2001|last1 = McDonald|first1 = James R.|issue=1 |doi-access=free |bibcode=2001BAMS...82...63M }}{{cite web |url=https://www.spc.noaa.gov/publications/mccarthy/f-scale.pdf |title=NWS Tornado Surveys and the Impact on the National Tornado|last= McCarthy|first=Daniel |website=www.spc.noaa.gov }} and Tom Grazulis of The Tornado Project retroactively rated all known significant tornadoes (F2–F5 or causing a fatality) in the U.S. back to 1880.

The Fujita scale was adopted in most areas outside of the United Kingdom.{{citation needed|date=April 2012}}

On February 1, 2007, the Fujita scale was decommissioned, and the Enhanced Fujita Scale was introduced in the United States. The new scale more accurately matches wind speeds to the severity of damage caused by the tornado.{{Cite web |last=Center |first=Storm Prediction |title=NOAA's NWS Storm Prediction Center |url=https://www.spc.noaa.gov/efscale/ |access-date=2024-12-20 |website=www.spc.noaa.gov |language=EN-US}}

Though each damage level is associated with a wind speed, the Fujita scale is effectively a damage scale, and the wind speeds associated with the damage listed are not rigorously verified. The Enhanced Fujita Scale was formulated due to research that suggested that the wind speeds required to inflict damage by intense tornadoes on the Fujita scale are greatly overestimated. A process of expert elicitation with top engineers and meteorologists resulted in the EF scale wind speeds, but these are biased to United States construction practices. The EF scale also improved damage parameter descriptions.{{cn|date=May 2023}}

File:Fujita scale technical.svg

The original scale as derived by Fujita was a theoretical 13-level scale (F0–F12) designed to smoothly connect the Beaufort scale and the Mach number scale. F1 corresponds to the twelfth level of the Beaufort scale, and F12 corresponds to Mach number 1.0. F0 was placed at a position specifying no damage (approximately the eighth level of the Beaufort scale), in analogy to how Beaufort's zeroth level specifies little to no wind. From these wind speed numbers, qualitative descriptions of damage were made for each category of the Fujita scale, and then these descriptions were used to classify tornadoes.{{cite web|url=http://www.spc.noaa.gov/efscale/ |title=Storm Prediction Center|website=spc.noaa.gov|access-date=May 27, 2017}}

At the time Fujita derived the scale, little information was available on damage caused by wind, so the original scale presented little more than educated guesses at wind speed ranges for specific tiers of damage. Fujita intended that only F0–F5 be used in practice, as this covered all possible levels of damage to frame homes as well as the expected estimated bounds of wind speeds. He did, however, add a description for F6, which he called an "inconceivable tornado", to allow for wind speeds exceeding F5 and possible advancements in damage analysis that might show it.

Based on aerial photographs of the damage it caused, Fujita assigned the strongest tornado of the 1974 Super Outbreak, which affected Xenia, Ohio, a preliminary rating of F6 intensity ± 1 scale.{{cite web|url = https://www.weather.gov/media/ohx/PDF/fujita_april31974.pdf|last = Fujita| first = T. Theodore|title = Jumbo Tornado Outbreak of 3 April 1974|year = 1974}} The 1977 Birmingham–Smithfield F5 tornado's damage was surveyed by Ted Fujita and he "toyed with the idea of rating the Smithfield tornado an F6".{{cite web |title=April 4, 1977, Smithfield F5 Tornado |url=https://www.weather.gov/bmx/event_04041977 |publisher=National Weather Service |access-date=8 April 2022}} In 2001, tornado expert Thomas P. Grazulis stated in his book F5–F6 Tornadoes; "In my opinion, if there ever was an F6 tornado caught on video, it was the Pampa, Texas tornado of 1995".{{cite book |author1=Thomas P. Grazulis |title=F5-F6 Tornadoes |date=2021 |publisher=The Tornado Project}} In 2023, it was announced by the Storm Prediction Center and National Weather Service Norman, Oklahoma that the 1970 Lubbock tornado was originally rated F6, which was later downgraded to its official rating of F5.{{cite journal |author1=Roger Edwards (SPC) |author2=Matthew S. Elliott (SPC) |author3=Patrick T. Marsh (SPC |author4=Douglas A. Speheger (NWS) |title=Errors, Oddities and Artifacts in U.S. Tornado Data, 1995–2021 |journal=Storm Prediction Center Publications |pages=1–10 |url=https://www.spc.noaa.gov/publications/edwards/oddities.pdf |access-date=11 January 2023}}

Furthermore, the original wind speed numbers have since been found to be higher than the actual 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. NOAA 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."[http://www.spc.noaa.gov/faq/tornado/ Tornado FAQ]. [http://www.spc.noaa.gov Storm Prediction Center]. Site accessed June 27, 2006.

The Tornado Project, headed by tornado expert Thomas P. Grazulis, states in reference to the F6 rating, [i]f 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.{{cite web |url=https://www.tornadoproject.com/cellar/fscale.htm |title=The Fujita Scale |website=The Tornado Project |location=St. Johnsbury, Vermont |date=2015 }}

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The six categories are listed here, in order of increasing intensity.

• The rating of any given tornado is of the most severe damage to any well-built frame home or comparable level of damage from engineering analysis of other damage.
• Since the Fujita scale is based on the severity of damage resulting from high winds, a tornado exceeding F5 is an immeasurable theoretical construct. Frame-home structural damage cannot exceed total destruction and debris dispersal, which constitutes F5 damage. Tornadoes with wind speeds over {{cvt|319|mph|km/h}} are possible and such extreme gusts have been determined using mobile radar observation, but no tornado has received an official damage-based F6 rating.

In 1973, Allen Pearson added additional path length and path width parameters to the Fujita scale. Under this version, each tornado would be assigned one Fujita scale rating and two Pearson scale ratings. For example, a tornado rated F4 based on damage with a path length of {{convert|63|mi|km}} and a path width of {{convert|800|yd|m}} would be rated F,P,P 4,4,4. Use of the Pearson scales was not widespread, however, and it remained more common to simply list a tornado's path length and path width directly.

For purposes such as tornado climatology studies, Fujita scale ratings may be grouped into classes.{{cite book|last=Grazulis|first=Thomas P.|author-link= Thomas P. Grazulis |title=Significant Tornadoes 1680–1991|date=July 1993|publisher=The Tornado Project of Environmental Films|location=St. Johnsbury, Vermont|isbn= 978-1-879362-03-1 }}[http://www.tornadoproject.com/fscale/fscale.htm The Fujita Scale of Tornado Intensity], Archived at: {{webarchive|url=https://web.archive.org/web/20111230005516/http://www.tornadoproject.com/fscale/fscale.htm |date=December 30, 2011}}{{cite web|url=http://www.nssl.noaa.gov/hazard/|title=index|first=Harold|last=Brooks|website=nssl.noaa.gov|access-date=May 27, 2017|archive-url=https://web.archive.org/web/20121004084424/http://www.nssl.noaa.gov/hazard/|archive-date=October 4, 2012|url-status=dead}}

{{main article|Enhanced Fujita scale}}

The Fujita scale, introduced in 1971 as a means to differentiate tornado intensity and path area, assigned wind speeds to damage that were, at best, educated guesses.{{cite book | last = Fujita| first = Tetsuya Theodore| author-link = T.T. Fujita| title = Proposed characterization of tornadoes and hurricanes by area and intensity| publisher = University of Chicago| year = 1971| location = Chicago }} Fujita and others recognized this immediately and intensive engineering analysis was conducted through the rest of the 1970s. This research, as well as subsequent research, showed that tornado wind speeds required to inflict the described damage were actually much lower than the F-scale indicated, particularly for the upper categories. Also, although the scale gave general descriptions of damage a tornado could cause, it gave little leeway for strength of construction and other factors that might cause a building to sustain more damage at lower wind speeds. Fujita tried to address these problems somewhat in 1992 with the Modified Fujita Scale,{{cite web|url=http://www.spc.noaa.gov/efscale/|title=NOAA's NWS Storm Prediction Center|first=Storm Prediction|last=Center|website=www.spc.noaa.gov|access-date=May 27, 2017}} but by then he was semi-retired and the National Weather Service was not in a position to update to an entirely new scale, so it went largely unenacted.{{cite book | last = Fujita| first = Tetsuya Theodore| author-link = Ted Fujita| title = Memoirs of an Effort to Unlock the Mystery of Severe Storms| publisher = University of Chicago| year = 1992| location = Chicago }}

In the United States, on February 1, 2007, the Fujita scale was decommissioned in favor of what scientists believe is a more accurate Enhanced Fujita Scale. The meteorologists and engineers who designed the EF Scale believe it improves on the F-scale on many counts. It accounts for different degrees of damage that occur with different types of structures, both manmade and natural. The expanded and refined damage indicators and degrees of damage standardize what was somewhat ambiguous. It also is thought to provide much better estimates of wind speeds and sets no upper limit on the wind speeds for the highest level, EF5. Environment Canada began using the Enhanced Fujita scale in Canada on April 1, 2013.[http://www.theweathernetwork.com/news/storm_watch_stories3&stormfile=Assessing_tornado_damage__EF-scale_vs._F-scale_19_04_2013?ref=ccbox_homepage_topstories Assessing tornado damage: EF-scale vs. F-scale] . Toronto has seen several tornados since the 1900s.

{{webarchive|url=https://web.archive.org/web/20130427003723/http://www.theweathernetwork.com/news/storm_watch_stories3%26stormfile%3DAssessing_tornado_damage__EF-scale_vs._F-scale_19_04_2013?ref=ccbox_homepage_topstories |date=April 27, 2013 }} The U.S. and Canada are the only countries to officially adopt the Enhanced Fujita scale.

{{Portal|Weather|Physics}}

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• Enhanced Fujita scale
• International Fujita scale
• Lists of tornadoes and tornado outbreaks
• List of F5 and EF5 tornadoes
• Rohn Emergency Scale for measuring the magnitude (intensity) of any emergency
• Saffir–Simpson Hurricane Scale
• Severe weather terminology (United States)
• Tornado intensity and damage
• Tornado records
• TORRO scale
• Wind engineering

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{{reflist}}

• {{cite journal | last1 = Marshall | first1 = Timothy P. | author-link = Timothy P. Marshall | year = 2001 | title = Birth of the Fujita Scale | journal = Storm Track | volume = 24 | issue = 3| pages = 6–10 }}
• {{cite journal |last = Edwards |first = Roger |author-link= Roger Edwards (meteorologist) |author2=J. G. LaDue |author3=J. T. Ferree |author4=K. Scharfenberg |author5=C. Maier |author6=W. L. Coulbourne |title = Tornado Intensity Estimation: Past, Present, and Future |journal = Bull. Amer. Meteor. Soc. |volume = 94 |issue = 5 |pages = 641–653 |year = 2013 |doi = 10.1175/BAMS-D-11-00006.1 |bibcode = 2013BAMS...94..641E |s2cid = 7842905 |doi-access = free }}

• [http://www.spc.noaa.gov/faq/tornado/ef-scale.html Enhanced F Scale for Tornado Damage] (SPC)
• [http://www.spc.noaa.gov/efscale/ The Enhanced Fujita Scale (EF Scale)] (SPC)
• [https://repository.library.noaa.gov/view/noaa/7317 A Guide for Conducting Convective Windstorm Surveys] (NWS SR146)
• [https://repository.library.noaa.gov/view/noaa/7227 The Tornado: An Engineering-Oriented Perspective] (NWS SR147)
• [http://www.lib.utexas.edu/taro/ttusw/00271/tsw-00271.html Fujita archival records] (Texas Tech University)

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Category:Hazard scales

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