May 31, 2011
A tornado is a violent, rotating column of air extending from a thunderstorm to the ground. According to the National Oceanic and Atmospheric Administration, they cause about 60 deaths and 1,500 injuries a year.
The revised scale was developed at Texas Tech University in conjunction with engineers, meteorologists and others from the National Oceanic and Atmospheric Administration, which is the umbrella agency for the National Weather Service.
The scale number reflects a top three-second wind gust:
■ EF-0 65 mph to 85 mph: Peels surface off of some roofs, damages some gutters or siding, breaks branches off trees and knocks over shallow-rooted trees.
■ EF-1 86 mph to 110 mph: Roofs are severely stripped, mobile homes are flipped or badly damaged and windows and glass break.
■ EF-2 111 mph to 135 mph: Roofs are torn off well-constructed houses, foundations of frame houses move, and it destroys mobile homes, breaks large trees and lifts cars off the ground.
■ EF-3 136 mph to 165 mph: Well-constructed houses are destroyed, damage is severe to large buildings such as shopping centers, lifts heavy cars and carries away structures with weak foundations.
■ EF-4 166 mph to 200 mph: Levels houses, throws around cars.
■ EF-5 More than 200 mph: Well-constructed houses are carried away, cars are turned into missiles and even steel-reinforced concrete is badly damaged. High-rise buildings have their structures deformed.