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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4.3.12.5. Geographic Scope of Hazard Blc <br />A typical extreme wind -producing non - <br />convective event may affect well over <br />100,000 square miles with wind damage U ,, <br />and may produce extreme impacts over <br />e ONAM , <br />tens of thousands of square miles. The h �� e /NG W <br />wo "n <br />total footprint may resemble those of �y ort lip <br />:i %/%i/ i; <br />derechos, but the time signature is very <br />Ni/ 10ai� different because non -convective events <br />i <br />y al, 1 <br />often affect large areas simultaneously „ a „ �,It ,/ <br />and for much longer durations than 110 W/ �Io a <br />PR <br />convective weather systems. <br />I viol a ,% <br />M11111111 > oot i <br />Non -convective extreme winds have been'"� <br />recorded in every state, but their impacts <br />are greatest in heavily populated areas, <br />even though their frequencies and <br />magnitudes may be greatest on the open Number of non -convective high wind fatalities in the lower48 <br />Plains of the central US. The highest death United States during the period 1980-2005. Source: <br />rates per unit area are found in the <br />http://earthzine.orgl2011/06/04/death from -a -clear -blue -sky - <br />extreme -non -convective -high -winds/ (modified from Ashley and <br />northeastern US, between Maryland and Black2oos) <br />New York state, where "nor'easters" can <br />expose large, dense populations to hurricane -force (or greater) winds, and along the Pacific coast. Death <br />rates in these regions are 10 times higher than in Minnesota and the Upper Midwest, because of higher <br />frequencies of intense low-pressure systems, the complex topography found between the mountains and <br />coasts induce wind -enhancing terrain effects, and the much greater population concentrations. <br />Within the Midwest, Minnesota appears to lie on the northwestern side of a risk corridor, which <br />maximizes near Chicago. <br />4.3.12.6. Chronologic patterns (seasons, cycles, rhythm) <br />Non -convective extreme winds associated with strong low-pressure areas are most common during the <br />fall and spring transition seasons, when the polar jet stream's mean track is near the Upper Midwest and <br />when continental temperature gradients are strong. Although strong cyclone development is more <br />common in spring than in fall, the conditions favoring explosive intensification are more common during <br />autumn, and thus, October and November have by far the highest frequency for non -convective extreme <br />winds. <br />4.3.12.7. Historical data/previous occurrence Bld <br />The record of non -convective extreme wind events in Minnesota is incomplete, owing to the lack of <br />adequate instrumentation, documentation, and categorization. Knowing the true frequency of extreme <br />winds in Minnesota would help estimate the likely recurrence of impacts on the modern landscape and <br />population. The following events are those known to have produced significant non -convective wind <br />impacts in Minnesota and the surrounding region. <br />191 <br />