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   - LOCATIONS OF TORNADOES

          In the United States

          In France and Belgium

    - PERIOD OF TORNADOES

CONSEQUENCES

During a tornado the damage is due to wind as well as an extremely sudden drop in pressure. Indeed, during the passage of the tornado the differences in air pressure cause buildings to explode outward when a tornado passes over them. Trapped air in houses has on all corners of rooms (windows, doors, and walls) a pressure that tends to explode outward. The violence of the wind increases damage to buildings. The instability of the wind direction, greatly amplifies the consequences of its speed. These large eddies can pick up debris several kilometers high and several kilometers away.

Despite advances in detection and alert systems for tornadoes, which reduced the number of deaths, mortality and damage caused by tornadoes are always high at the regional level.

Tornadoes are certainly one of the most important meteorological phenomena in the United States, given the number of tornadoes observed in this country. Among the 800 tornadoes observed on average each year in the United States, only about twenty can be classified as severe (F4 or F5). Since 1950 the average number of victims is more than 100 dead and many tens of millions of dollars in damage.

TORNADO ONTNSITIES ARE CLASSIFIED ON FUJITA SCALE

Scale	maximum winds	Consequences
F0	70 mph (120 km/h)	twisted antennas, branches broken off trees, displaced caravans...
F1	110 mph (180 km/h)	draws water, mobile homes pushed off foundations or overturned, uprooted trees,...
F2	150 mph (250 km/h)	raised roofs, broken light structures, large trees snapped or uprooted,...
F3	205 mph (330 km/h)	Roofs and some walls torn off well-constructed houses, trains overturned, large projectiles,...
F4	260 mph (420 km/h)	Well-constructed houses leveled, structures with weak foundations relocated, cars thrown and large projectiles generated,...
F5	315 mph (520 km/h)	Strong frame houses lifted off foundations and carried considerable distance to disintegrate, automobile-sized projectiles hurtle through the air in excess of 100 yards, trees debarked, other incredible phenomena expected,...

Tornadoes are ranked in the Fujita Tornado Scale according to wind speed.

 

Here's a video with a duration of 54 minutes.

Aerial view of damages in Oklahoma
city Devastated after a tornado in 1999