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• <br />• <br />• <br />Anoka County Multi - Jurisdictional <br />All Hazards Mitigation Plan <br />ground. A bolt of lightning reaches a temperature approaching 50,000 degrees in a split second. <br />In the United States, 75 to 100 citizens are killed each year by lightning. Lightning's electrical <br />charge and intense heat electrocutes on contact, splits trees and ignites fires. <br />Hail is produced by many strong thunderstorms and is a product of the updrafts and downdrafts <br />that develop inside the clouds of a thunderstorm where super cooled water droplets exist. The <br />transformation of droplets to ice requires a temperature below 32 degrees, and a catalyst in the <br />form of tiny particles of solid matter, or freezing nuclei. Hail can be smaller than a pea or as <br />large as softballs and can be destructive to property, crops, livestock, and people. <br />4.2.1.9 Severe Weather - Tornados <br />Tornados are violent windstorms characterized by a <br />twisting, funnel- shaped cloud. A tornado is spawned by <br />a thunderstorm or hurricane and produced when cool air <br />overrides a layer of warm air, forcing the warm air to rise <br />rapidly. A funnel does not need to reach to the ground <br />for a tornado to be present. A debris cloud beneath a <br />thunderstorm is all that is needed to confirm the <br />presence of a tornado. The damage from a tornado is a <br />result of the high wind velocity and wind -blown debris. <br />Tornados can occur at any time of the year; however, <br />the season is generally March through August. Over <br />80% of all tornadoes strike between noon and midnight. <br />The most violent tornadoes are capable of tremendous <br />destruction with wind speeds of 250 mph or more. <br />Damage paths can be in excess of 1 mile wide and 50 <br />miles long. Even with advances in meteorology, adequate warning time <br />or sometimes not possible. <br />for tornadoes <br />is short <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 />Fujita— Pearson Tornado Scale Description Table <br />F- <br />Scale <br />Damage <br />Winds <br />(mph) <br />Description <br />F -0 <br />Light <br />40 -72 <br />Chimney damage, tree branches broken <br />F -1 <br />Moderate <br />73 -112 <br />Mobile homes overturned <br />F -2 <br />Considerable <br />113 -157 <br />Considerable damage, trees downed, mobile homes demolished <br />F -3 <br />Severe <br />158 -206 <br />Roofs /walls torn down, trains and cars overturned <br />F -4 <br />Devastating <br />207 -260 <br />Well- constructed walls leveled <br />F -5 <br />Incredible <br />261 -318 <br />Homes lifted off foundation and carried considerable distances <br />F -6 <br />Inconceivable <br />319 -379 <br />Unknown <br />81 <br />