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"In an average year, 800 tornadoes are reported nationwide, resulting in 80 deaths and over 1,500 injuries." TORNADOES...Nature's Most Violent Storms. A Preparedness Guide. NOAA. When and Where: Whenever and wherever conditions are right, tornadoes are possible, but they are most common in the central plains of North America, east of the Rocky Mountains and west of the Appalachian Mountains. They occur mostly during the spring and summer; the tornado season comes early in the south and later in the north. They usually occur during the late afternoon and early evening. However, they have been known to occur in every state in the United States, on any day of the year, and at any hour. They also occur in many other parts of the world, including Australia, Europe, Africa, Asia, and South America. Appendix A includes tornado statistics for the US compiled by the Storm Prediction Center. What: Tornadoes come from the energy released in a thunderstorm. As powerful as they are, tornadoes account for only a tiny fraction of the energy in a thunderstorm. What makes them dangerous is that their energy is concentrated in a small area, perhaps only a hundred yards across. Not all tornadoes are the same, of course, and science does not yet completely understand how part of a thunderstorm's energy sometimes gets focused into something as small as a tornado. How: Research has revealed that tornadoes usually form under certain types of atmospheric conditions. Those conditions can be predicted, but not perfectly. When forecasters see those conditions, they can predict that tornadoes are likely to occur. However, it is not yet possible to predict in advance exactly when and where they will develop, how strong they will be, or precisely what path they will follow. The damage from tornadoes comes from the strong winds they contain. It is generally believed that tornadic windspeeds can be as high as 300 mph in the most violent tornadoes. Windspeeds that high can cause automobiles to become airborne, rip ordinary homes to shreds, and turn broken glass and other debris into lethal missiles. The biggest threat to living creatures (including humans) from tornadoes is from flying debris and from being tossed about in the wind. Tornadoes are classified according to the damage they cause. Through observational studies, T. Theodore Fujita created the following scale in the late 1960's to classify tornadoes. The scale correlates wind speeds with damage: F-0 is the weakest and F-5 the strongest. Scale MPH Expected Damage F-0 40-72 Light Damage F-1 73-112 Moderate Damage F-2 113-157 Considerable Damage F-3 158-206 Severe Damage F-4 207-260 Devastating Damage F-5 261-318 Incredible Damage Point to the link to see the corresponding image. Best viewed by Netscape 3.0 and above. For others, see Appendix B for graphical representation of the F-scale For information on tornado safety consult the National Weather Service Publication List on weather safety. Once a tornado is formed and has been detected, warnings can be issued based on the path of the storm producing the tornado. Why: The reason behind the Verification of the Origins of Rotation in Tornadoes EXperiment a.k.a. Chapter 2 1