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<br />Ramsey County | Multi-Jurisdiction Hazard Mitigation Plan 64 <br />Figure 14. Tornado Alley <br /> <br />3.11.3 EXTENT <br />Winds are classified by the National Weather Service (NWS) using the categories shown in Table 10. <br />Table 10. Wind Speed Classifications <br />Description Speed <br />Strong Wind Gusts Between 39 mph and 57 mph <br />Damaging Wind Gusts Between 58 mph and 74 mph causing minor damage <br />Very Damaging Wind Gusts Between 75 mph and 91 mph causing moderate <br />damage <br />Violent Wind Gusts Greater than 92 mph causing major damage <br />Source: www.weather.gov <br />Since 2007, tornado strength in the United States has been ranked based on the Enhanced Fujita scale <br />(EF scale), replacing the Fujita scale introduced in 1971. The EF scale, shown in Table 11 uses similar <br />principles to the Fujita scale, with 6 categories from 0-5, based on wind estimates and damage caused <br />by the tornado. The EF Scale is used extensively by the NWS in investigating tornadoes (all tornadoes are <br />now assigned an EF Scale number), and by engineers in correlating damage to buildings and techniques