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The term "tornado preparedness" refers to safety precautions made before the arrival of and during a tornado. Historically, the steps taken have varied greatly, depending on location, or time remaining before a tornado was expected. For example, in rural areas, people might prepare to enter an external storm cellar, in case the main building collapses, and thereby allow exit without needing rescue from the main building as in urban areas. Because tropical storms have spawned many tornadoes, hurricane preparations also involve tornadoes. The term "tornado preparedness" has been used by government agencies, emergency response groups, schools,〔 "Tornado Preparedness Tips for School Administrators", NOAA.gov, 2010, web: (NOAA-sch ). 〕 insurance companies, and others. == Understanding the dangers == Preparedness involves knowing the major dangers to avoid. Some tornadoes are the most violent storms in nature.〔 "Tornado", FEMA.gov, August 2010, web: (FEMA-tornado ). 〕 Tornadoes have varied in strength, and some tornadoes have been mostly invisible due to a lack of loose dirt or debris in the funnel cloud.〔 Spawned from severe thunderstorms, tornadoes have caused fatalities and devastated neighborhoods within seconds of arrival. A tornado operates as a rotating, funnel-shaped cloud that extends downward from a thunderstorm, to the ground, with swirling winds which have reached .〔 The wind speed might be difficult to imagine: traveling the length of a U.S. football field within 1 second〔 A speed of 300 miles per hour is 300 *5280 = 1,584,000 feet per hour, or 440 feet (134 m) per second. 〕 (over per second). Damage paths have been in excess of and .〔 Not all tornadoes are easily seen. A tornado funnel can be transparent until reaching an area with loose dirt and debris.〔 Also, some tornadoes have been seen against sunlit areas, but rain or nearby low-hanging clouds has obscured other tornadoes. Occasionally, tornadoes have developed so suddenly, so rapidly, that little, if any, advance warning was possible.〔 Before a tornado strikes an area, the wind has been known to die down and the air to become very still.〔 A cloud of debris has sometimes marked the bottom of a tornado even when the funnel was not visible. Tornadoes typically occur along the trailing edge of a thunderstorm. The following is a summary of typical tornadoes:〔 : * They may strike quickly, with little or no warning. : * They may appear nearly transparent until dust and debris are picked up or a cloud forms in the funnel. : * The average tornado moves Southwest to Northeast in the U.S., but tornadoes have been known to move in any direction. : * The average forward speed of a tornado is , but has varied from stationary to . : * Tornadoes can also accompany tropical storms and hurricanes as they move onto land. : * Waterspouts are tornadoes that form over water. : * Tornadoes are most frequently reported east of the Rocky Mountains during spring and summer months. : * Peak tornado season in the southern U.S. states is March through May; in the northern states, it is late spring through early summer. : * Tornadoes are most likely to occur between 3 p.m. and 9 p.m. (local time), but have occurred at other times.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tornado preparedness」の詳細全文を読む スポンサード リンク
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