Tornado comes from the verb « to turn » in Spanish. The tornado is a howling wind whirl, which develops close to a storm updraft, when the howling wind of lower atmosphere changes its direction and strength. Small tornadoes can also arise from storm clouds.

Various phenomenons can stem from a tornado, which is identified when the rotating air touches the ground. If it does not touch the ground, the tornado is a tunnel-shaped cloud, on water, it is a waterspout, and if there are no clouds, it is called a dust devil.

What is peculiar to tornadoes is its trajectory, always unpredictable and which is only depending on drafts making them follow an undetermined corridor.

In the United-States, there are between 800 and 1,200 tornadoes each year, out of which a score reaches F4 and F5 on the Fujita Scale (winds between 330 and 500 km/h). The State of Florida is the state with the most frequent tornadoes.

In France, there are about a hundred waterspouts on the littoral zones, but tornado risks are weaker than in the US.

The strongest tornado ever seen in the history is the “Tri-State-Tornado” which crossed three American states (Missouri, Illinois and Indiana) in March 1925. It holds all records: its trajectory, 325 km, its duration, it lasted about 3 hours 30 minutes, and its speed, about 117km/h!

Eventually, an event occurred in 1974, called the “Super Outbreak”, where, during more than 18 hours, 148 tornadoes took shape in the Midwest and in the South of Canada, out of which 30 were among the tempestuous (a record of F4 and F5). It seems that, at one point, 16 tornadoes hit the ground at the same time!