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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />of precipitation, with isolated reports of over 5 inches, resulting in flooded intersections, submerged <br />roads, and minor damage to businesses and residences. The locations receiving the heaviest rainfall were <br />in the same position with respect to the cyclone center as areas that often receive the most intense non - <br />convective winds; fortunately, however, this storm did not produce such winds, and there were few or no <br />compound flooding/extreme wind effects. <br />December 15, 2021 <br />An unusual winter situation unfolded <br />during this evening as a muggy airmass <br />and a developing cyclone produced <br />intense thunderstorms that raced <br />northeastward from Nebraska into <br />southeastern Minnesota, producing 22 <br />tornadoes in the state, along with <br />extensive straight-line wind damage. <br />After the storms cleared the area, the <br />intensifying low-pressure system" <br />responsible for them approached, with E e-like eature seen in eastern Nebraska on December15 2021 <br />Y J` , as <br />an "eye -like" center of circulation and severe thunderstorms advance through southeastern Minnesota and <br />a large area of strong non -convective intense non -convective winds move northeastward with the circulation. <br />winds. The winds moved into the same <br />areas damaged by the severe thunderstorms. Rochester, for instance, recorded 77 mph wind gusts with <br />the severe thunderstorms, and then three hours of 55-70 mph non -convective gusts, with another peak <br />of 77 mph just before midnight local time. Throughout southern Minnesota, non -convective wind gusts <br />reached 60-75 mph, producing tens of thousands of power outages as a much colder air mass settled into <br />the region. <br />The non -convective winds were quite strong, especially considering the severe weather barrage they had <br />followed, but the peak winds remained below the levels of those witnessed in 1949 and 1998, likely <br />because this cyclone was not quite as intense, and because it was still gaining strength as the strongest <br />winds passed through Minnesota. <br />4.3.12.8. Future trends/likelihood of occurrence Ble <br />Non -convective high winds are relatively rare, occurring, on average, fewer than three times per year in <br />Minnesota. Extreme events are even rarer, and only affect some part of the state approximately once or <br />twice per decade. Open areas of the state in the west and south are more conducive to extreme <br />thunderstorm winds than other areas, but extreme non -convective winds do not appear to follow that <br />pattern. If anything, extreme winds, and especially the impacts of them, are slightly more common in the <br />hilly and tree -filled eastern parts of the state than on the open prairies. <br />The frequency of non -convective extreme wind in Minnesota is directly tied to the frequency of intense <br />mid -latitude or extratropical cyclones. Unfortunately, the physical link between explosive cyclogenesis <br />(the process that leads to intense low-pressure systems) and human -caused climate change, is not well <br />understood, so research into the future of these systems has been inconclusive, with results depicting all <br />possible scenarios. <br />198 <br />