Fujita scale
F0 < 73 mph Light damage
F1 73–112 mph Moderate damage
F2 113–157 mph Considerable damage
F3 158–206 mph Severe damage
F4 207–260 mph Devastating damage
F5 261–318 mph Incredible damage

The Fujita scale (F-Scale; /fuˈtə/), or Fujita–Pearson scale (FPP 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 (cycloidal marks), 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.[1][2]

Background

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,[3] 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[4][5] 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.[6] The Fujita scale was adopted in most areas outside of the United Kingdom.[citation needed]

On February 1, 2007, the Fujita scale was decommissioned, and the Enhanced Fujita Scale was introduced in the United States.[7] The new scale more accurately matches wind speeds to the severity of damage caused by the tornado.

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 aren't 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.

Derivation

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.[8] The diagram on the right illustrates the relationship between the Beaufort, Fujita, and Mach number scales.

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.[9] 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.[10] 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.”[11]

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."[9] Since then, the Enhanced Fujita Scale has been created using better wind estimates by engineers and meteorologists.

Parameters

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

Scale Wind speed estimate[7] Frequency[12] Potential damage[7]
mph km/h
F0 40–72 64–116 44.14% Light damage.
Small trees are blown down and bushes are uprooted. Shingles are ripped off roofs, windows in cars and buildings are blown out, medium to large branches snapped off of large trees, sheds are majorly damaged, and loose small items are tossed and blown away (i.e. lawn chairs, plastic tables, sports equipment, mattresses). Barns are damaged.
This house only sustained minor loss of shingles. Though well-built structures are typically unscathed by F0 tornadoes, falling trees and tree branches can injure and kill people, even inside a sturdy structure.
F1 73–112 117–180 34.24% Moderate damage.
Roofs stripped from shingles or planting. Small areas of roof may be blown off house. Doors and garage doors blown in, siding ripped off houses, mobile homes flipped or rolled onto their sides, small trees uprooted, large trees snapped or blown down, telephone poles snapped, outhouses and sheds blown away. Cars occasionally flipped or blown over, and moderate roof and side damage to barns. Corn stalks slightly bent and stripped of leaves.
F1 tornadoes cause major damage to mobile homes and automobiles and can cause minor structural damage to well-constructed homes. This frame home sustained major roof damage, but otherwise remained intact.
F2 113–157 181–253 16.17% Significant damage.
Whole roofs ripped off frame houses, interiors of frame homes damaged, small and medium trees uprooted. Weak structures such as garages, barns, and mobile homes are completely destroyed.
At this intensity, tornadoes have a more significant impact on well-built structures, removing the roofs, and collapsing some exterior walls of poorly built structures. F2 tornadoes are capable of completely destroying mobile homes and generating large amounts of flying debris. This home completely lost its roof, but its walls remained intact.
F3 158–206 254–332 4.35% Severe damage.
Roofs and numerous outside walls blown away from frame homes, all trees in its path uprooted and/or lofted, two-story homes have their second floor destroyed, highrises have many windows blown out, radio towers blown down, metal buildings (i.e. factories, power plants, and construction sites) are heavily damaged, sometimes completely destroyed. Large vehicles such as tractors, buses, and forklifts are blown from their original positions.
Here, the roof and all but some inner walls of this frame home have been demolished. While taking shelter in a basement, cellar, or inner room improves one
F4 207–260 333–418 1.00% Devastating damage.
Trees partially debarked, cars are mangled and thrown in the air, frame homes are completely destroyed and some may be swept away, trains are blown off railroad tracks, and barns are leveled.
Brick homes get reduced to piles of rubble. Above-ground structures are almost completely vulnerable to F4 tornadoes, which level well-built structures, toss heavy vehicles through the air, and uproot trees, turning them into flying missiles.
F5 261–318 419–512 0.10% Incredible damage.
Cars are mangled and thrown hundreds, possibly thousands of yards away. Frame homes, brick homes, and small businesses are swept away, trees debarked, corn stalks flattened or ripped out of the ground, skyscrapers sustain major structural damage, grass ripped out of the ground. Wood and any small solid material become dangerous projectiles.
These tornadoes cause complete destruction, obliterating and sweeping away almost anything in their paths, including those sheltering in open basements, sending any vehicles or trains flying through the air, and causing tall buildings to collapse or to have severe structural deformations.

Pearson scales

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 63 miles (101 km) and a path width of 800 yards (730 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.[6]

Pearson scales
Scale Path length Path width
<0.3 mi (0.48 km) <6 yd (5.5 m)
P0 0.3–0.9 mi (0.48–1.45 km) 6–17 yd (5.5–15.5 m)
P1 1.0–3.1 mi (1.6–5.0 km) 18–55 yd (16–50 m)
P2 3.2–9.9 mi (5.1–15.9 km) 56–175 yd (51–160 m)
P3 10–31 mi (16–50 km) 176–566 yd (161–518 m)
P4 32–99 mi (51–159 km) 0.3–0.9 mi (0.48–1.45 km)
P5 100–315 mi (161–507 km) 1.0–3.1 mi (1.6–5.0 km)

Rating classifications

Tornado rating classifications
F0 F1 F2 F3 F4 F5
Weak Strong Violent
Significant
Intense

For purposes such as tornado climatology studies, Fujita scale ratings may be grouped into classes.[6][13][14]

Decommissioning in the U.S.

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.[15] 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,[16] 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.[17]

In the United States, on February 1, 2007,[1] 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.[18] The U.S. and Canada are the only countries to officially adopt the Enhanced Fujita scale.

See also

References

  1. ^ a b "Fujita Tornado Damage Scale". spc.noaa.gov. Retrieved May 27, 2017.
  2. ^ "Fujita Scale - Tornado Damage Scale". factsjustforkids.com. Retrieved June 14, 2019.
  3. ^ https://www.spc.noaa.gov/publications/edwards/ef-scale.pdf[bare URL PDF]
  4. ^ McDonald, James R. (2001). "American Meteorological Society". Bulletin of the American Meteorological Society. 82 (1): 63–72. Bibcode:2001BAMS...82...63M. doi:10.1175/1520-0477(2001)000<0063:TTFHCT>2.3.CO;2.
  5. ^ McCarthy, Daniel. "NWS TORNADO SURVEYS AND THE IMPACT ON THE NATIONAL TORNADO" (PDF). www.spc.noaa.gov.
  6. ^ a b c Grazulis, Thomas P. (July 1993). Significant Tornadoes 1680–1991. St. Johnsbury, Vermont: The Tornado Project of Environmental Films. ISBN 978-1-879362-03-1.
  7. ^ a b c Fujita Tornado Damage Scale Storm Prediction Center. Accessed May 20, 2009.
  8. ^ "Storm Prediction Center". spc.noaa.gov. Retrieved May 27, 2017.
  9. ^ a b Tornado FAQ. Storm Prediction Center. Site accessed June 27, 2006.
  10. ^ Fujita, T. Theodore (1974). "Jumbo Tornado Outbreak of 3 April 1974" (PDF).
  11. ^ "April 4, 1977, Smithfield F5 Tornado". National Weather Service. Retrieved April 8, 2022.
  12. ^ "Storm Prediction Center WCM Data". Storm Prediction Center. Retrieved September 15, 2021.
  13. ^ The Fujita Scale of Tornado Intensity, Archived at: Archived December 30, 2011, at the Wayback Machine
  14. ^ Brooks, Harold. "index". nssl.noaa.gov. Archived from the original on October 4, 2012. Retrieved May 27, 2017.
  15. ^ Fujita, Tetsuya Theodore (1971). Proposed characterization of tornadoes and hurricanes by area and intensity. Chicago: University of Chicago.
  16. ^ Center, Storm Prediction. "NOAA's NWS Storm Prediction Center". www.spc.noaa.gov. Retrieved May 27, 2017.
  17. ^ Fujita, Tetsuya Theodore (1992). Memoirs of an Effort to Unlock the Mystery of Severe Storms. Chicago: University of Chicago.
  18. ^ Assessing tornado damage: EF-scale vs. F-scale Archived April 27, 2013, at the Wayback Machine

Bibliography