In the United States, tornadoes primarily occur in the spring and summer east of the Rocky Mountains. According to the NOAA National Severe Storms Laboratory, in an average year, 800 tornadoes get reported nationwide. Those tornadoes result in an average of 80 deaths and more than 1,500 injuries per year. Tornadoes also accompany hurricanes and tropical storms in other parts of the country.
A tornado consists of a rapidly rotating column of air reaching down from a thunderstorm to the ground. Also known as funnel clouds, tornadoes can cause severe damage, especially with violent tornadoes reaching wind speeds of 250 miles per hour or more. The paths of destruction can reach in excess of one mile wide and 50 miles long. Tornadoes that form over warm water are called waterspouts. Waterspouts rarely cause damage unless they move inland where they become tornadoes.
The most common method used to determine tornado damage is based on the enhanced F-scale. The method looks at damage to 28 different types of buildings and trees. Then the method uses the most intense damage within the path of the tornado to determine the strength, with F5 indicating the most violent tornado.
The size or shape of a tornado does not indicate its strength. Instead, tornadoes get classified as weak, strong or violent storms according to several factors, including wind speed. Seventy percent of all deaths occur during violent tornadoes, which may last up to an hour. Yet violent tornadoes make up just 2 percent of all tornadoes.
Many people think rivers, lakes and mountains remain safe from tornadoes, but this is false. According to NOAA, a tornado went through Yellowstone National Park in the 1980s, causing vast destruction on a 10,000 foot mountain. Many people think they should open their windows when the threat of a tornado appears. Instead of opening windows that allow the violent winds to enter the structure, head for a safe place instead. One last myth to dispel involves the fact that low pressure causes buildings to explode when the tornado passes by. Damage actually gets caused by the violent winds and debris ramming into the structure, not low pressure.
One of the deadliest tornadoes took place in March 1925. The tornado moved between 60 to 73 miles per hour for 219 miles across parts of Missouri, Illinois and Indiana, producing F5 damage and killing 695 people. According to NOAA, one of the largest outbreaks of tornadoes occurred on April 3 and 4, 1974, when 147 tornadoes touched down in 13 states and moved into Canada. The tornadoes killed 318 people and caused 5,454 injuries in the United States alone. The tornado that caused the most damage occurred in Topeka, Kansas in June 1966. Damage from that tornado, adjusted for inflation, reached more than $1.5 billion in 2007 dollars.
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