International Fujita scale

The International Fujita scale (abbreviated as IF-Scale) rates the intensity of tornadoes and other wind events based on the severity of the damage they cause.[1] 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.

In 2018, the first draft version of the IF-scale, version 0.10 was published. This version was based on a 12-step rating scale. Over the next few years, dozens of tornadoes would be rated on this version of the scale. Most notably, the 2021 South Moravia tornado received a rating (IF4) and full damage survey on the IF-scale conducted by ESSL, the Czech Hydrometeorological Institute and four other organizations.[2] On May 6th, 2023, version 0.99.9d was published, which changed it to a 9-step rating scale.[3] In late July 2023, the first official version of the IF scale was published.[4]

2018 version
See also: List of tornadoes rated on the 2018 International Fujita scale
Tornado rating classifications[5]
IF0- IF0 IF0+ IF1- IF1 IF1+ IF2- IF2 IF2+ IF3 IF4 IF5
Weak Strong Violent
Significant
Intense

Parameters

The 12 categories for the International Fujita 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. However, for the actual IF-scale in practice, damage indicators (the type of structure which has been damaged) are predominantly used in determining the tornado intensity. The IF-scale steps are defined by a central value and an error. The errors have been estimated to be 30% of the central value, resulting in overlapping speed ranges. The distances between the central values of the steps have been so chosen that the upper bound exceeds the central value of the next step, ensuring a balance between the resolution of the scale and the expected errors. Since ESSL required that the steps be consistent with the original Fujita scale, they introduced steps with – and + suffixes indicating steps one third higher or lower than the central value of the original scale, e.g. F1- equals “F2 - 1⁄3F2” and F2+ equals “F2 + 1⁄3F2”. Above F2, such a subdivision was not introduced and only full steps are used.

Scale Wind speed
(Estimated)
mph km/h m/s
IF0- 45 ± 1472 ± 2220 ± 6
IF0 56 ± 1790 ± 2725 ± 7
IF0+ 67 ± 20108 ± 3230 ± 9
IF1- 70 ± 24128 ± 3836 ± 11
IF1 92 ± 28149 ± 4541 ± 12
IF1+ 106 ± 32170 ± 5147 ± 14
IF2- 120 ± 36193 ± 5854 ± 16
IF2 135 ± 40217 ± 6560 ± 18
IF2+ 150 ± 45241 ± 7267 ± 20
IF3 182 ± 55293 ± 8881 ± 24
IF4 234 ± 70376 ± 113105 ± 31
IF5 290 ± 87466 ± 140130 ± 39

2023 version

On May 6, 2023, version 0.99.9d was published, which changed it to a 9-step rating scale.[3] In this version, the wind speed damage indicator was introduced, which made it the first tornado intensity and damage scale to use measured wind speeds and Doppler weather radar measured wind speeds.[3] When the first official publication of the IF scale, the 9-step rating scale was kept. It was noted that each scale’s wind speed is to be taken with a 20% error margin on each side of the central value.[4] This was done to ensure the lower or upper bound of the overlapping rating came close to the central value of the other rating.[4]

Tornado rating classifications[6]
IF0 IF0.5 IF1 IF1.5 IF2 IF2.5 IF3 IF4 IF5
Weak Strong Violent
Significant
Intense
Scale Wind speed
(Estimated)
(Central value; Full range of the 20% error margin)
mph km/h m/s
IF0 55; 44–6690; 72–10825; 20–30
IF0.5 75; 60–90120; 96–14433; 27–40
IF1 90; 72–108150; 130–18040; 32–48
IF1.5 110; 88–132180; 144–21650; 40–60
IF2 135; 108–162220; 176–26460; 48–72
IF2.5 160; 128–192250; 200–30070; 56–84
IF3 180; 144–216290; 232–34880; 64–96
IF4 230; 184–276380; 304–456105; 84–126
IF5 290; 232–348470; 376–564130; 104–156

Damage indicators, subclasses, and degrees of damage

The IF scale currently has 23 damage indicators (DI), each with a varying number of subclasses and degrees of damage (DoD).[4][3]

DI Abbr.Damage indicator (DI)SubclassesDegrees of damage
BSBuilding - structure A, AB, B, C, D, E, F 0, 1A, 1B, 2
BRBuilding - roof A, AB, B, C, D, E, F 0, 1, 2
BNBuilding - non-structural elements SW, SS, TW, TS, HW, HS 0, 1, 2, 3
BMBuilding - anchoring SM, SI, DB 1
VHRoad Vehicles C, E, L, T 0, 1, 2, 3, 4
TRTrees W, A, S 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
TSTree stands WA, S 0, 1, 2, 3, 4
WTWind turbines A, S 0, 1, 2, 3
GHGreenhouses W, A, S 0, 1, 2, 3
TCTrain cars S, F 0, 1
MHMobile homes / Static caravans – 0, 1, 2, 3, 4, 5
PTPoles and towers W, S, T 0, 1, 2
SPSolar Panels – 0, 1
FCFences W, S 0, 1
FWFree-standing walls Z, A, AB, B, C, D, E, F 1, 2
SNSigns and billboards T, M 0, 1, 2
SWConnected scaffolding – 1
CPCarports / garages – 1
SSService Station Canopies – 0, 1, 2, 3
SCShipping Containers A, B, C, D, E, F 1, 2, 3
CRCranes G, t 1, 2
OFOutdoor Furniture L, H 0, 1, 2
WMWind Speed Measurement See section below See section below

DI: Wind Speed Measurement

A unique feature of the International Fujita scale compared to the Fujita or Enhanced Fujita scale is a new damage indicator based on measured wind speeds. For the IF scale, only wind speeds measured at or below 10 metres (11 yd) can be used to determine a rating. Doppler weather radar measurements are also able to be used to determine a rating if they are measured within damaging distance. For radar measurements, any readings below 60 metres (66 yd) can be used to determine a rating.[4][3]

Three second measurement

For three-second wind speed measurements, it is assumed to be an average of 88.8% of the three-second measurement.[4][3]

Degree of Damage (DoD) / Measured IF# Speed Three Second Measurement
mph km/h m/s
DoD 0 / IF0 42.5–5669–9119–25
DoD 0.5 / IF0.5 57–74.592–12026–32
DoD 1 / IF1 73.9–90119–14633–40
DoD 1.5 / IF1.5 91–109147–17640–49
DoD 2 / IF2 110–129177–20850–57
DoD 2.5 / IF2.5 129–156.5209–24258–70
DoD 3 / IF3 151–183.9243–29668–82
DoD 4 / IF4 184–231297–37383–103
DoD 5 / IF5 ≥232≥374≥104

Two second measurement

For two-second wind speed measurements, it is assumed to be an average of 90.9% of the two-second measurement.[4][3]

Degree of Damage (DoD) / Measured IF# Speed Two Second Measurement
mph km/h m/s
DoD 0 / IF0 43.4–5870–9420–26
DoD 0.5 / IF0.5 59–7495–12027–33
DoD 1 / IF1 75–93121–15034–40
DoD 1.5 / IF1.5 93–111.8150–18042–50
DoD 2 / IF2 111.8–132180–21351–59
DoD 2.5 / IF2.5 133–154214–24860–68
DoD 3 / IF3 154–188249–30369–84
DoD 4 / IF4 188–237304–38285–106
DoD 5 / IF5 ≥238≥383≥107

One second measurement

For one-second wind speed measurements, it is assumed to be an average of 92.5% of the one-second measurement.[4][3]

Degree of Damage (DoD) / Measured IF# Speed One Second Measurement
mph km/h m/s
DoD 0 / IF0 44.1–5871–9520–26
DoD 0.5 / IF0.5 59–7696–12327–34
DoD 1 / IF1 77–94124–15235–42
DoD 1.5 / IF1.5 95–113153–18343–51
DoD 2 / IF2 114–134184–22052–60
DoD 2.5 / IF2.5 135–156218–25261–70
DoD 3 / IF3 157–191253–30871–85
DoD 4 / IF4 192–241309–38886–107
DoD 5 / IF5 ≥241.5≥389≥108

Zero second measurement

For zero-second wind speed measurements, it is assumed to be an instantaneous wind speed measurement.[4][3] This can only be used if it was 10Hz or higher sample rate.[4][3][7]

Degree of Damage (DoD) / Measured IF# Speed Zero Second Measurement
mph km/h m/s
DoD 0 / IF0 47.8–6477–10322–28
DoD 0.5 / IF0.5 64–82104–13229–36
DoD 1 / IF1 82–101.9133–16437–45
DoD 1.5 / IF1.5 102–123165–19846–55
DoD 2 / IF2 124–145199–23456–65
DoD 2.5 / IF2.5 146–169235–27366–75
DoD 3 / IF3 170–207274–33376–92
DoD 4 / IF4 208–260334–42093–116
DoD 5 / IF5 ≥261≥421≥117

See also

References
  1. "The International Fujita (IF) Scale Tornado and Wind Damage Assessment Guide" (PDF). ESSL.org. European Severe Storms Laboratory. Retrieved 26 June 2022.
  2. Tomás Púcik; David Rúva; Miroslav Singer; Miloslav Stanëk; Pieter Groenemeijer (23 June 2022). "Damage Survey of the Violent Tornado in Southeast Czechia on 24 June 2021" (PDF). European Severe Storms Laboratory. pp. 1–31. Retrieved 16 May 2023.
  3. "The International Fujita (IF) Scale" (PDF). European Severe Storms Laboratory. Retrieved 8 May 2023.
  4. Pieter Groenemeijer (ESSL); Lothar Bock (DWD); Juan de Dios Soriano (AEMet); Maciej Dutkiewicz (Bydgoszcz University of Science and Technology); Delia Gutiérrez-Rubio (AEMet); Alois M. Holzer (ESSL); Martin Hubrig; Rainer Kaltenberger; Thilo Kühne (ESSL); Mortimer Müller (Universität für Bodenkultur); Bas van der Ploeg; Tomáš Púčik (ESSL); Thomas Schreiner (ESSL); Miroslav Šinger (SHMI); Gabriel Strommer (ESSL); Andi Xhelaj (University of Genova) (30 July 2023). "The International Fujita (IF) Scale" (PDF). European Severe Storms Laboratory. Retrieved 30 July 2023.
  5. "Severe Thunderstorm Climatology". Archived from the original on 2012-10-04. Retrieved 2022-07-17.
  6. "Severe Thunderstorm Climatology". Archived from the original on 2012-10-04. Retrieved 2022-07-17.
  7. A. C. M. Beljaars (1 December 1987). "The Influence of Sampling and Filtering on Measured Wind Gusts". Journal of Atmospheric and Oceanic Technology. 4 (4): 613–626. doi:10.1175/1520-0426(1987)004<0613:TIOSAF>2.0.CO;2. ISSN 1520-0426. Retrieved 16 May 2023.
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