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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />Power Outages and Intense Heat — Some of the most intense summer thunderstorm winds and <br />the explosive class of "progressive derechos" tend to occur on the fringes of major heat waves. <br />The heat and deep moisture often pool near the boundary that promotes the development of <br />thunderstorms, and those ingredients <br />act to fuel <br />hintensification <br />te lthe storms and thedevelopment of <br />destructive winds.rY"; it iiU1y <br />When thunderstorm winds damage the <br />electrical infrastructure during or prior <br />to intense heat waves, residents are left <br />without the benefit of air-conditioning <br />while having to deal with intense heat. <br />This sort of cascading effect occurred in <br />the Ohio Valley and eastern US on June <br />29, 2012, when a derecho traveled for <br />700 miles, impacting 10 states and <br />Washington, D.C. An estimated 4 million <br />customers lost power for up to a week. <br />The region impacted by the derecho was <br />also during a heat wave, which claimed <br />34 lives in areas without power following <br />the derecho. <br />This map illustrates the large-scale meteorological <br />environment favorable for progressive and serial <br />derechos on the northern or western fringe of a high- <br />pressure area associated with a major heat wave over <br />central and eastern United States. <br />Wildland Fires — Extreme straight-line winds and derechos can obliterate millions of trees across <br />miles of forest due to the extreme winds associated with them. This increases fuel loads on <br />forests and escalates the risk of wildland fire. <br />Tornadoes — Extreme straight-line winds and tornadoes can and do occur with the same <br />convective system at times. In addition to the December 15, 2021, event discussed above, <br />damaging straight-line winds and tornadoes also occurred near each other in or close to Hennepin <br />County on July 3, 1983, July 1, 1997, and September 21, 2005. <br />The tornadoes may occur with isolated supercells ahead of the derecho producing squall line, or <br />they may develop from storms within the squall line itself. Tornadoes have occurred with serial <br />derechos, as on December 15, 2021, and on May 12, 2022, in southwestern Minnesota, and they <br />have also occurred with progressive derechos, as on July 3, 1983. <br />Blizzards — It has yet to be documented in Minnesota, but any cold -season derecho is likely to be <br />associated with a vigorous low-pressure system and it would be possible for not just cold air, but <br />intense snow and wind, to follow damaging thunderstorms within 6 to 48 hours. <br />84 <br />