A tornado is a powerful, twisting windstorm. The most violent winds that occur on earth are the tornado winds with speeds of 200 mph. A tornado is a rotating funnel cloud that extends downward from a mass of dark clouds. Its violent winds can carry automobiles, destroy buildings, and uproot huge trees. The winds of a tornado whirl in a counterclockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere.
No one is sure how tornadoes form. We do now that they occur because of instability in the atompshopere. They generally occur during severe thunderstorms or along a warm or cold front. Tornadoes begin as a horizontal twisting of air in a thunderstorm. This twisting of air somehow becomes vertical and a tornado is formed. Tornadoes occur most often in the Spring but can occur during any season of the year. They occur most often in the United States in the Great Plains. This area of the country is know as Tornado Alley.
Although most of the tornadoes that occur in the United States occur in Tornado Alley, every state has had tornadic activity. Tornadoes can and have occurred in every State of the United States. The red shaded area on the map shows the region know as Tornado Alley. The greatest number of tornadoes occur in the United States. Most of the F4 and F5 tornaodes also occur in the United States. Tornadoes are classified according to the Fujita Scale. This is a scale that ranks tornadoes according to strength of the winds. The scale goes from a F1 to a F5 ( see the chart below).
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