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<br />Ramsey County | Multi-Jurisdiction Hazard Mitigation Plan 82 <br />Table 21. 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: National Weather Service <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 22 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 <br />with different wind speeds caused by tornadoes. It uses three-second gusts estimated at the point of <br />damage based on a judgment of damage. <br />When tornado-related damage is surveyed, it is compared to a list of Damage Indicators (DIs) and <br />Degrees of Damage (DoD) which help estimate better the range of wind speeds the tornado likely <br />produced. Each damage indicator is rated on a scale of 1-8 DoD. From that, a rating (from EF0 to EF5) is <br />assigned. <br />Table 22. Enhance Fujita Scale <br />EF Rating 3 Second Gust (mph) Description <br />0 65-85 Light damage. Some damage to chimneys; branches broken <br />off trees; shallow-rooted trees pushed over; sign boards <br />damaged. <br />1 86-110 Moderate damage. Peels surface off roofs; mobile homes <br />pushed off foundations or overturned; moving autos blown <br />off roads. <br />2 111-135 Considerable damage. Roofs torn off frame houses; mobile <br />homes demolished; boxcars overturned; large trees snapped <br />or uprooted; light-object missiles generated; cars lifted off <br />ground. <br />3 136-165 Severe damage. Roofs and some walls torn off well- <br />constructed houses; trains overturned; most trees in forest <br />uprooted; heavy cars lifted off the ground and thrown. <br />4 166-200 Devastating damage. Well-constructed houses leveled; <br />structures with weak foundations blown away some <br />distance; cars thrown, and large missiles generated. <br />5 200+ Incredible damage. Strong frame houses leveled off <br />foundations and swept away; automobile-sized missiles fly <br />through the air in excess of 100 meters (109 yds); trees <br />debarked; incredible phenomena will occur. <br />Source: National Weather Service