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• Electric power outage; <br />• Surface and air transportation disruption; <br />• Telecommunications system outage; <br />• Human health and safety; <br />• Psychological hardship; and <br />• Economic disruption. <br />Indian River County's vulnerability to tornadoes is compounded <br />by the high concentration of mobile home residents in large <br />mobile home communities. According to the 2000 U.S. <br />Census, there are 6,786 mobile homes in Indian River County, <br />representing 11.7% of the total housing units in the County. <br />Three municipalities within Indian River County have significant <br />concentrations of mobile homes. Sebastian has a total of <br />564 mobile homes, representing 7.6% of the total housing <br />units. Wabasso has a total of 166 mobile homes, representing <br />31.9% of the total housing units. Fellsmere has a total of 397 <br />mobile homes, representing 42.4% of the total housing units. <br />Risk Assessment. Historical data indicate the overall <br />vulnerability of Indian River County to tornadoes is low, but <br />some specific communities have a moderate to high <br />vulnerability to this hazard due to the type of construction or <br />numbers of mobile homes (manufactured housing units) within <br />their boundaries. These communities include Sebastian, <br />Wabasso, and Fellsmere. <br />Tornado risk is defined as the annual probability of significant <br />structural damage and is divided into four probabilities of <br />occurrence: <1 in 500, 1 in 500, 1 in 200, and 1 in 100. <br />d. Severe Thunderstorm/Lightning — Hazard Identification <br />A severe thunderstorm is defined as a thunderstorm containing <br />one or more of the following phenomena: hail of at least 1 inch, <br />surface wind speeds of 58 miles per hour or greater, or any <br />combination of those two criteria (NOAA, NWS, 2014). Severe <br />weather can include lightning, tornadoes, damaging straight- <br />line winds, and large hail. Most individual thunderstorms only <br />last several minutes; however, some can last several hours. <br />Long-lived thunderstorms are called super cell thunderstorms. <br />A super cell is a thunderstorm that has a persistent rotating <br />updraft. This rotation maintains the energy release of the <br />thunderstorm over a much longer time than typical, pulse -type <br />Indian River County Comprehensive Emergency Management Plan Basic Page 27 <br />