The International Fujita scale (abbreviated as IF-Scale) is a scale that rates the

intensity of tornadoes 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 inferre ...

and other wind events based on the severity of the damage they cause. It is used by the

European Severe Storms Laboratory The European Severe Storms Laboratory (ESSL) is a scientific organisation that conducts research on severe convective storms, tornadoes, intense precipitation events, and avalanches across Europe and the Mediterranean. It operates the widely co ...

(ESSL) and various other organizations including (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 In the evening hours of June 24, 2021, a rare, violent, and deadly long-tracked tornado struck several villages in the Hodonín District, Hodonín and Břeclav District, Břeclav districts of the South Moravian Region of the Czech Republic, kil ...

received a rating (IF4) and full damage survey on the IF-scale conducted by ESSL, the

Czech Hydrometeorological Institute The Czech Hydrometeorological Institute (CHMI; ) is the central state office of the Czech Republic in the fields of air quality, meteorology, climatology and hydrology. It is an organization established by the Ministry of the Environment of the Cz ...

and four other organizations. On May 6, 2023, version 0.99.9d was published, which changed it to a 9-step rating scale. In late July 2023, the first official version of the IF scale was published.

2018 version

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. IF2- equals "IF2 - 1⁄3IF2" and IF2+ equals "IF2 + 1⁄3IF2". Above F2, such a subdivision was not introduced and only full steps are used.

2023 version

On May 6, 2023, version 0.99.9d was published, which changed it to a 9-step rating scale. 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 A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pu ...

measured wind speeds. 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. This was done to ensure the lower or upper bound of the overlapping rating came close to the central value of the other rating.

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).

DI: Wind Speed Measurement

A unique feature of the International Fujita scale compared to the Fujita or

Enhanced Fujita scale The Enhanced Fujita scale (abbreviated EF-Scale) is a scale that rates tornado intensity based on the severity of the damage a tornado causes. It is used in the United States and France, among other countries. The EF scale is also unofficially ...

is a new damage indicator based on measured wind speeds. For the IF scale, only wind speeds measured at or below can be used to determine a rating.

measurements are also able to be used to determine a rating if they are measured within damaging distance. For radar measurements, any readings below can be used to determine a rating.

Three second measurement

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

Two second measurement

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

One second measurement

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

Zero second measurement

For zero-second wind speed measurements, it is assumed to be an

instant In physics and the philosophy of science, instant refers to an infinitesimal interval in time, whose passage is instantaneous. In ordinary speech, an instant has been defined as "a point or very short space of time," a notion deriving from its etym ...

aneous wind speed measurement. This can only be used if it was 10 Hz or higher sample rate.

References

{{reflist Hazard scales Wind Tornado Scales in meteorology