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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4.3.3.5. Geographic Scope of Hazard Blc <br />Hennepin County is within a high -frequency corridor for extreme thunderstorm winds and derechos that <br />covers much of the eastern half of the US. <br />Every part of the county has experienced r5, <br />significant damage from unusually intense' <br />thunderstorm winds. Within the county,µ <br />there are no favored areas. Winds estimated°�k ��� �� ,� <br />h d <br />to 80 mph hit downtown Minneapolis in Aprils <br />of 1986, tearing a hole in the roof of the�w�� <br />Metrodome. Winds at least that strong winds <br />have hit ever corner of the count with 100 <br />Y Y, <br />mph winds measured at the international <br />airport in 1951, and winds likely well over 100 „�„� <br />mph striking the northern suburbs in July of <br />1983.F <br />Nationally, derechos most commonly occur <br />along two axes. One track parallels the "Corn4� <br />Belt" from the upper Mississippi Valley <br />southeast into the Ohio Valley; the other Approximate number of times "moderate and high intensity" <br />extends from the southern Plains northeast (MH) derechos affected points in the United States during the <br />into the mid -Mississippi Valley. During the years 1980 through 2001. Areas affected by 3 or more derecho <br />cool season (September through April), events are shaded in yellow, orange, and red. <br />derechos are relatively infrequent but are <br />most likely to occur from east Texas into the southeastern states. Although derechos are rare west of the <br />Great Plains, derechos occasionally do occur over interior portions of the western United States, especially <br />during spring and early summer. <br />The highest annual frequencies of occurrence appear along the "Corn Belt," from Minnesota and Iowa <br />into western Pennsylvania, and in the south-central states, from eastern parts of the southern Plains into <br />the lower Mississippi Valley. However, the frequencies vary by season. During the warm season (May <br />through August), derecho events are most frequent in the western part of the Corn Belt. During the <br />remainder of the year (September through April), the maximum frequencies shift south into the lower <br />Mississippi Valley <br />4.3.3.6. Chronologic patterns (seasons, cycles, rhythm) <br />Extreme straight-line winds and derechos in the United States are most common in the late spring and <br />summer (May through August), with more than 75% occurring between April and August. The seasonal <br />variation of derechos corresponds rather closely with the incidence of thunderstorms. However, as noted <br />above, Minnesota (and neighboring states) experienced extreme straight-line winds qualifying as a <br />derecho on December 15, 2021. <br />85 <br />