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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />Hundreds of thousands of people may lose power for a week or more, as happened most recently in 2013. <br />In addition, unlike the localized damage produced by a tornado, often covering the equivalent of one <br />square mile, extreme thunderstorm wind damage can be widespread, affecting tens or even hundreds of <br />square miles within the county. As a result, repairs often require substantial effort, with additional delays <br />related to shortages in supplies. <br />Extreme straight-line winds also can expose socio-economic vulnerabilities among Hennepin County's <br />diverse and growing population. Derechos and severe thunderstorms can strike quickly, posing serious <br />challenges to the elderly, or anyone with limited mobility who is caught outside. Those new to the region <br />who are unfamiliar with severe weather, how to access information about it, and how to respond, may <br />be caught off -guard and unprepared for the dangerous winds. Language barriers also may prevent some <br />people from getting vital information as the storm is approaching. Anyone without adequate shelter will <br />be subject to all the risks of being outside during dangerous thunderstorm winds. In general, extreme <br />thunderstorm winds pose greater threats to disadvantaged populations that may lack the resources <br />others have to anticipate, plan for, seek shelter from, and recover from extreme straight-line winds. <br />4.3.3.4. Potential for cascading effects <br />• Flash Flooding - On occasion, the convective system responsible extreme wind damage will stall, <br />back -build, or regenerate, producing excessive rainfall. In other cases, the storm may simply <br />unload enormous quantities of rainfall. On July 1, 1997, a complex of thunderstorms produced <br />80-110 mph winds and extensive damage from Wright into western Hennepin County, while <br />dropping 3-5 inches of rain in 60-90 minutes over much of the area. The rains flooded every type <br />of road in the county, submerging vehicles and significantly delaying emergency vehicles deployed <br />to respond to the extreme wind event. <br />• Power Outages and Arctic Outbreaks — Dangerously cold air had never been considered a serious <br />concern in relation to extreme thunderstorm winds and derechos, which tend to form during the <br />warm season. On December 15, 2021, however, a historic outbreak of intense thunderstorm <br />winds and tornadoes struck southeastern Minnesota, knocking out power for 1-3 days as <br />temperatures in the 10s F settled into the region. <br />Any extreme straight-line wind occurring outside the usual warm season, and particularly <br />between November and March, may pose significant cold weather risks in its aftermath. Without <br />power, electrical baseboard heat will not operate, nor will many appliances, security systems, <br />electronic devices, or lights. <br />83 <br />