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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />Hazard Assessment: WINTER STORM, BLIZZARD, EXTREME SNOWFALL <br />4.3.11.1. Definition <br />Winter storms produce intense <br />snowfall rates and/or large <br />accumulations that can <br />immobilize entire regions and <br />paralyze cities, stranding <br />commuters, closing airports, <br />stopping the flow of supplies, <br />and disrupting emergency and <br />medical services. The weight of <br />snow can cause roofs to <br />collapse and knock down trees <br />and power lines. Homes, farms, <br />and businesses may be isolated <br />for days. The cost of snow <br />removal, repairing damages, Cars on Excelsior Boulevard after 1940 "Armistice Day Blizzard." Courtesy W <br />and the loss of business can MN Historical Society <br />have severe economic impacts <br />on counties and municipalities. In Hennepin County, virtually all winter storms are generated by the <br />convergence of moisture and cold temperatures associated with low-pressure systems. <br />Blizzards represent the most dangerous class of winter storms, combining strong winds with falling or <br />freshly fallen snow to reduce visibility for a period of time. Technically, they are defined as three hours or <br />more of sustained winds or frequent gusts of 35 mph or higher in falling or blowing snow, and visibilities <br />reduced to a quarter mile or less. The strong winds create deadly whiteout conditions that bring traffic to <br />a standstill, enabling the wind -driven snow to form dangerous drifts that are impossible for many vehicles <br />to pass. In addition, the strong winds are often accompanied by falling temperatures and low wind chills, <br />subjecting stranded motorists to life -threatening conditions that may persist for 24 hours or more. Lastly, <br />the strong winds of blizzards exert additional stress upon structures if they were already straining under <br />the load of heavy snow. <br />All winter storms have some combination of cold air, moisture, and lifting mechanisms that turn the <br />moisture into precipitation. Most winter storms affecting Hennepin County are associated with <br />extratropical cyclones (low-pressure systems). Typically, the heaviest snow and blizzard conditions are <br />found on the left side of the path of the storm system. <br />169 <br />