Tornadoes generate the most powerful winds on Earth, sometimes in excess of 300 miles per hour, about twice as fast as those of hurricanes. In America each year there are on average about 800 tornadoes, with over 80 deaths and 1,500 injuries. In May 1999, an unusually violent set of tornadoes broke out in and around Oklahoma City, killing nearly 50 people in one day. Researchers clocked winds at 318 mph, believed to be the fastest ever recorded. The largest number of tornadoes ever recorded in a single outbreak was in April 1974 outbreak when 148 tornadoes hit 13 states and parts of Canada killing 316 people in less than 24 hours.

   Tornadoes can occur on any day of the year and any place in the nation, but they are most likely from April through June, and develop as you would expect from the nickname most frequently up and down "Tornado Alley", the states of the Great Plains including Kansas and Oklahoma, and from Northern Texas up to Illinois. The southern states are more likely to experience tornadoes early in the year, and northern states in later months. The United States has more tornadoes than any place else on Earth, but they can also be found in Australia, Europe, Southern Asia, especially Bangladesh and India, Africa and South America. 7 out of 10 tornadoes are relatively weak, with winds of less than 100 mph, and die out very quickly, often without causing extensive damage. Winds in less than 2% of tornadoes exceed 200 mph.

   Tornadoes are spawned by violent thunderstorms, and also by hurricanes. They are defined as being a funnel cloud stretching from the surface up into a storm. They deliver a punch much less powerful than the total energy contained in the whole thunderstorm or hurricane that gives birth to them, but what makes them particularly deadly is that their energy is packed into a very small area. A tornado may be the size of just a city block, less than half a kilometer, while a hurricane (like Floyd in 1999) may be the size of a state as large as Texas. Most tornadoes last only minutes (though the May 99 Oklahoma tornadoes lasted for 4 hours: the record is 7 hours!), while hurricanes endure for days as they churn across the ocean and continue, while weakening, over coastal areas.

   Within that relatively small area of violent destruction, tornadoes kill by sucking up heavy objects as large as cars and even trucks and railroad cars, and throwing them, like heavy weapons, through buildings. That's why the most important safety precaution is to TAKE SHELTER in basements or special shelters, and NEVER to venture out when a tornado is forecast.

   As you'll see in the LIVE FROM THE STORM videos, NOAA's storm chasers from the National Severe Storms Laboratory (NSSL) in Norman, OK, are extremely careful even as they try to gather the detailed information that is essential to make tornado predictions more reliable and provide longer lead time for people to take cover. One of the most important tools in understanding what actually triggers tornadoes (which the researchers call "tornado genesis", the birth of tornadoes) from thunderstorms is Doppler radar. Tornado warnings can now be given as much as 30 minutes in advance, thanks to researchers' recognition of key warning signs that a tornado is likely. They hope to make that lead time one hour as they study tornadoes more with the latest tools, and understand them better.

   As you might also guess from the fact that they are called "twisters" (and yes, the feature movie "Twister" was based in part on the research done at NSSL), what triggers tornadoes is a very special set of circumstances that set air violently rotating.

Glossary Links: Downdrafts, Doppler Radar, Hurricane, Tornado Alley , Waterspouts
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Tornado Alley Tornado Season

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