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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />�Hazard Assessment: TORNADO <br />4.3.2.1. Definition <br />4.3.2.2. Range of Magnitude <br />Tornadoes can appear in a variety of shapes and sizes ranging from large wedge shapes with a diameter <br />greater than a mile down to thin rope like circulations. The strongest tornadoes can have wind speeds <br />more than 200 mph. Tornado wind speeds are estimated after the fact based on the damage they <br />produce. Tornadoes are characterized on a scale of 0 (weakest) to 5 (strongest) according to the Enhanced <br />Fujita (EF) Scale. The original Fujita Scale was devised in 1971 by Dr. Ted Fujita of the University of Chicago. <br />The scale gives meteorologist the ability to rate from FO to F5 based upon the type and severity of damage <br />that the tornado produced. At that time, there were very few actual measurements of tornado wind <br />speeds that he could relate to the damage, but Dr. Fujita used them together with a lot of insight to devise <br />approximate wind speed ranges for each damage category. <br />In subsequent years, structural engineers have examined damage from many tornadoes. They use <br />knowledge of the wind forces needed to damage or destroy various buildings and their component parts <br />to estimate the wind speeds that caused the observed damage. What they found was that the original <br />Fujita Scale wind speeds were too high for categories F3 and higher, which may have led to inconsistent <br />ratings, including possible overestimates of associated wind speeds. <br />With these inconsistent ratings in mind, a panel of meteorologists and engineers convened by the Wind <br />Science and Engineering Research Center at Texas University devised the new Enhanced Fujita Scale, <br />which became active as of February 1, 2007. The EF Scale incorporates more damage indicators and <br />degrees of damage than the original "F" Scale, allowing more detailed analysis and better correlation <br />between damage and wind speed. You can see both scale charts below TABLE 4.3.2A. <br />.• <br />