Fujita scale

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.

[7] The new scale more accurately matches wind speeds to the severity of damage caused by the tornado.

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.

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.

[11] 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.

NOAA notes that "precise wind speed numbers are actually guesses and have never been scientifically verified.

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

[6][17][18] 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.

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.