The United States typically has more tornadoes than anywhere else in the world, although they can occur just about anywhere, says the US National Weather Service (NWS). The states of the great American plains such as Kansas, Oklahoma and Texas are particularly affected.
The mechanism behind the formation of a tornado is not yet fully known to scientists, but it excites a category of enthusiasts dubbed
storm chasers, ready to risk their lives to film them.
The mystery remains great around tornadoes. They are rare, deadly and difficult to predict, says the US National Oceanic and Atmospheric Agency (NOAA) National Severe Storms Laboratory.
What is known, however, is that they are generally the result of so-called thunderstorms
supercell, which are characterized in particular by strong updrafts, says NOAA.
Within the storm, a strong vertical wind shear causes the appearance of a cylinder which rotates horizontally on itself.
Upward air currents lift the rotating cylinder within the supercell.
The rotating column of air becomes thinner, thus often stretching in the shape of a funnel, and spins faster and faster to form a tornado, also details NOAA.
Tornadoes grow extremely quickly and can dissipate just as quickly, according to the NWS.minutes “,” text “:” Most tornadoes make landfall for less than 15 minutes “}} ‘>Most tornadoes make landfall for less than 15 minutes, he continues.
Tornadoes are the most severe storms in nature, underlines the NWS. Winds from a tornado can thus reach nearly 500 km / h, with damage reaching nearly two kilometers wide and about 80 km long for each tornado.
According to NOAA, more than 50 people are killed each year in the United States by tornadoes.
Spring 2011 was the deadliest US tornado season, with more than 580 people killed between April and June. The damage bill had risen to $ 21 billion.
After a tornado has passed, scientists assess its strength by observing the damage caused and associating it with the observed gusts. They then classify it using the improved Fujita scale, which includes six degrees – from 0 to 5 -, 0 being light damage with gusts between 100 and 135 km / h, and 5 being damage.
unbelievable with gusts in excess of 320 km / h.