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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />areas affected will be at risk for non -convective high or extreme winds, generally beginning 6-24 <br />hours after the severe weather. This occurred in south-central and southeast Minnesota on <br />December 15, 2021, when severe thunderstorm winds to 75 mph or greater knocked out power <br />and were followed by non -convective winds of 60-80 mph several hours later. <br />In these situations, any debris generated by the severe weather will have the potential to become <br />airborne and further scattered by the non -convective winds, prolonging the hazard exposure by <br />hours. Moreover, the sustained wind loadings will further weaken or damage already - <br />compromised structures, causing the potential for further collapse. The winds will also threaten <br />to blow down trees and power structures previously spared. Lastly, these intense non -convective <br />winds will add a layer of danger to ongoing search and rescue operations. <br />Blizzard — Although the very strongest winds tend to wrap into what had been the warm sector <br />and are often removed from the area of heavy snow, the broad area of strong and even dangerous <br />winds can reach back into areas experiencing (or previously experiencing) winter weather <br />conditions. In these cases, the wind hazards are compounded by falling temperatures, reduced <br />visibilities, and slippery or obstructed roads. Winds combined with heavy snowfall can knock <br />down trees, power lines and power poles, blocking streets and cutting some residents off from <br />their communities. <br />Cold — Even areas that do not experience blizzard conditions may see rapid temperature drops <br />behind the cold front. Because these events usually occur during the transition seasons, the <br />extent and depth of the cold air tend to be minimized. However, temperatures can fall near or <br />below zero, and wind chill temperatures can fall to -25 or lower. The cold weather risks are <br />greatest in areas that had lost power or utility service from extreme winds, as frostbite and <br />hypothermia become serious concerns. <br />Flash Flooding — Most of the systems capable of extreme winds move quickly enough that <br />precipitation amounts are kept under 2 inches. However, there have been instances of prolonged <br />heavy rainfall and at least minor flooding, raising the possibility of a joint flood/non-convective <br />wind disaster at some point in the future, though none have been recorded in Minnesota. The <br />force of moving water combined with sustained strong winds would easily overwhelm stranded <br />vehicles and would significantly hamper rescue operations. <br />Wildland Fires —The swaths of trees toppled by non -convective high winds can increase fuel loads <br />on forests and escalating the risk of wildland fire. Additionally, although most non -convective <br />wind systems produce some precipitation, many of the extreme winds come through "dry," and <br />even in fair conditions. If the system passes through during a drought or other condition with <br />unusually dry vegetation, the winds could easily enhance wildfire risk. Any existing fires would <br />have the potential to spread rapidly and uncontrollably. <br />190 <br />