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Lamar County Multi- Jurisdictional Hazard Mitigation Plan <br />Chapter Three <br />3. Extent <br />A worst case scenario involving thunderstorms would be a solid or redeveloping line of severe <br />thunderstorms that moves through the entire county. These storms can result in heavy rains <br />causing wide spread flooding and road closures. Large economic loss to agriculture and /or <br />major damage to buildings and other property can result if such storms are accompanied by hail <br />and high winds. High winds and lightning associated with such storms can also down trees and <br />highline poles and result in power outages capable of affecting large areas of the county. <br />Extreme winds can cause several kinds of damage to a building. Figure 3 below shows how <br />extreme winds affect a building and helps explain why these winds cause buildings to fail. Wind <br />speeds, even in these extreme wind events, rapidly increase and decrease. An obstruction <br />such as a house in the path of wind causes the wind to change direction. This change in wind <br />direction increases pressure on parts of the house. The combination of increased pressures <br />and fluctuating wind speeds creates stress on the house that frequently causes connections <br />between building components to fail. <br />Figure 3: Windstorm Effects on Structures <br />ow <br />Top <br />V" <br />wwK► a ON W"Ls <br />WWWOOI POMBUM A00* tO weal VAI"W <br />Buildings that fail under the effects of extreme winds often appear to have exploded, giving rise <br />to the misconception that the damage is caused by unequal wind pressures inside and outside <br />the building. This misconception has led to the myth that during an exteme wind event, the <br />windows and doors in a building should be opened to equalize the pressure. In fact, opening a <br />window or door allows wind to enter a building and increases the risk of building failure. <br />104 <br />