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Anoka County <br />MINNESOTA <br />Respectful, Innovative, Fiscally Responsible <br />Anoka County 2019 <br />Multi -Jurisdictional <br />All Hazards Mitigation Plan <br />4.3.1.4 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 to <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 />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 FO-F1 are considered weak, those classified as F2-F3 are <br />considered strong, while those classified as F4-F5 are considered violent. <br />Enhanced Fuiita Tornado Scale Description Table <br />EF- <br />Scale <br />Damage <br />Winds <br />(mph) <br />Description <br />EF-0 <br />Light <br />65-85 <br />Chimney damage, tree branches broken <br />EF-1 <br />Moderate <br />86-110 <br />Mobile homes overturned <br />EF-2 <br />Considerable <br />111-135 <br />Considerable damage, trees downed, mobile homes demolished <br />EF-3 <br />Severe <br />136-165 <br />Roofs/walls torn down, trains and cars overturned <br />EF-4 <br />Devastating <br />166-200 <br />Well -constructed walls leveled <br />EF-5 <br />Incredible <br />200 + <br />Homes lifted off foundation and carried considerable distances <br />The most violent tornadoes are capable <br />of tremendous destruction with wind <br />speeds of 250 mph or more. Damage <br />paths can be in excess of 1 mile wide <br />and 50 miles long. Even with advances <br />in meteorology, warning time for <br />tornadoes is short or impossible. <br />Tornadoes can occur in any state, but <br />are more frequent in the Midwest, <br />Southeast and Southwest. <br />Tornado season is generally March <br />through August, although tornadoes <br />can occur at any time of year. They <br />tend to occur in the afternoons and <br />evenings. Over 80% of all tornadoes <br />strike between noon and midnight. <br />There have been 24 tornado events <br />that have impacted Anoka County and <br />participating jurisdictions since 1961. In <br />some cases, the same tornado may <br />have impacted multiple jurisdictions and <br />was reported more than once. <br />98 <br />Minnesota Tornadoes <br />by County 1950-2018 <br />Red: 40 or more tornadoes <br />Blue: 30-39 tornadoes <br />Yellow: 20-29 tornadoes <br />Commented [REK113]: Updated 10-26-11 <br />Commented [RK114]: Update graphic <br />