Compléter TornadoesVersion en ligne Find the missing words while viewing the video. par david archambaud 1 spinning cloud Research form occur rip downdraft growing lift funnel speed over ground widest twisters destruction winds 300 devastation updraft top Tornadoes ? Big shaped clouds that can through a community and leave a wake of . They can in seconds , change direction in a heartbeat and their can last a lifetime . Exactly how and why tornadoes is still a bit of a mystery but an indication that one is forming is a wall . Fast - moving roll air below into a horizontal vortex above opposing surface winds , similar to a tube . Warmed by the Sun , buoyant air near the ground begins to a section of the horizontal vortex into a vertical position . The vortex extends toward the . As it picks up anything in its path can be ripped apart or thrown in the air . Upper - level winds tilt the rotating called a mesocyclone . This allows a storm to keep as warm air is sucked into the storm away from the cool . The vortex spins like a , sometimes up to miles per hour , and while some tornadoes move slowly , others can travel over the ground at speeds of 110 miles per hour . The tornado ever recorded , the May 2013 El Reno tornado in Oklahoma was 2 . 6 miles across . That's wider across than Manhattan ! has allowed us to identify essential ingredients needed for to form in the US . 2 60 deadliest continent peak levels damage recorded lives shelter pick uproot dangerous Warm cool scientists Alley scale air estimated dry 1989 average collide power moist typically from the Gulf of Mexico , air typically from Canada and air typically from the Rockies , when these air masses they create the perfect conditions for a tornado . Nearly three - quarters of the world's tornadoes occur in the United States and the season is between May and June . A majority touch down in Tornado , a section of the central United States but tornadoes have been in all 50 states and on every except Antarctica . Tornadoes are very and you should never underestimate their . The time between a tornado warning and a strike is at a mere 13 minutes , giving residents little time to seek . On average tornadoes killed people every year in the United States ! The tornado in history was not in the United States but a tornado that ripped through Bangladesh in , killing an estimated 1 , 300 people . We measure the amount of to land and property using the EF , which ranks tornadoes on six different . From zero a heavy breeze that can crops to level five , enough wind to up a house . It's the desire to better understand them that sends into the field year after year in search of answers that can hopefully save while putting theirs at risk .
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