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Anoka County Multi-Jurisdictional <br />All Hazards Mitigation Plan <br /> 98 <br /> <br />4.3.1.3 Severe Weather - Tornado <br />Tornados are violent windstorms characterized by a twisting, funnel-shaped cloud. Spawned by <br />a thunderstorm (or sometimes as a result of a hurricane), the funnel does not need to reach t o <br />the ground for a tornado to be present. A debris cloud beneath a thunderstorm is all that is <br />needed to confirm the presence of a tornado. The damage from a tornado is a result of the high <br />wind velocity and wind-blown debris. <br /> <br />The intensity, path length, and width of tornadoes are rated according to a scale developed by <br />T. Theodore Fujita and Allen D. Pearson. The Fujita-Pearson Tornado Scale is presented <br />below. Tornadoes classified as F0-F1 are considered weak, those classified as F2-F3 are <br />considered strong, while those classified as F4-F5 are considered violent. <br /> <br /> <br />Enhanced Fujita Tornado Scale Description Table <br />EF- <br />Scale Damage <br />Winds <br />(mph) Description <br />EF-0 Light 65-85 Chimney damage, tree branches broken <br />EF-1 Moderate 86-110 Mobile homes overturned <br />EF-2 Considerable 111-135 Considerable damage, trees downed, mobile homes demolished <br />EF-3 Severe 136-165 Roofs/walls torn down, trains and cars overturned <br />EF-4 Devastating 166-200 Well-constructed walls leveled <br />EF-5 Incredible 200 + Homes lifted off foundation and carried considerable distances <br /> <br />The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 <br />mph or more. Damage paths can be in excess of 1 mile wide and 50 miles long. Even with <br />advances in meteorology, warning time for tornadoes is short or impossible. Tornadoes can <br />occur in any state, but are more frequent in the Midwest, Southeast and Southwest. <br /> <br />Tornado season is generally March through <br />August, although tornadoes can occur at <br />any time of year. They tend to occur in the <br />afternoons and evenings. Over 80% of all <br />tornadoes strike between noon and <br />midnight. <br /> <br />There have been 36 tornado events that <br />have impacted Anoka County and <br />participating jurisdictions since 1951. In <br />some cases the same tornado may have <br />impacted multiple jurisdictions and was <br />reported more than once. These tornado <br />events resulted in 84 fatalities and 672 <br />injuries. The reported structure damage <br />was $104,465,290 and content damage <br />was estimated to be $18,679,500. <br /> <br />The city of Andover experienced tornadoes <br />in July of 1983 and September of 2005. In <br />the 1983 event 64 structures had significant <br />damage and hundreds of trees were