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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />3d Hazard Assessment: ICE STORMS <br />4.3.13.1. Definition <br />Ice storms are major winter weather events that produce <br />accumulations of ice, either from rain falling in sub -freezing <br />surface temperatures, or from heavy sleet. <br />In Minnesota and Hennepin County, ice storms form most <br />commonly ahead of a warm front, resulting in warm air being <br />lifted over colder air in place, producing precipitation that is <br />warm enough for rain but then freezes on contact with sub- <br />freezing objects. When the front is associated with strong low <br />pressure, the precipitation can be quite heavy, with rapid ice <br />accumulations. With weaker systems or when the front is <br />stationary, it may produce sustained light to moderate <br />precipitation for many hours. Either situation can lead to ice -related impacts. <br />Significant ice storm damage in southwestern <br />Minnesota in April 2013. Courtesy MPR. <br />If the layer of freezing air near the surface is deep enough, the precipitation will fall as sleet instead of <br />freezing rain. The granular nature of sleet generally makes it less of a damage and safety hazard than <br />freezing rain, but sleet is nevertheless often a part of major ice storms. <br />4.3.13.2. Range of magnitude <br />Magnitude of ice accumulation is rarely measured, and most accounts are purely anecdotal. Severe ice <br />storms in Minnesota have been reported to leave a glaze up to 3 inches thick. <br />4.3.13.3. Spectrum of consequences B2b <br />Heavy accumulations of ice can bring down trees, topple utility poles, and damage communications <br />towers, disrupting power and communications for days, while utility companies make extensive repairs. <br />Ice also damages roofs, gutters, and downspouts, and falling tree limbs often cause devastating secondary <br />damages to structures and vehicles. <br />Even small ice accumulations can be extremely dangerous for motorists and pedestrians, and ice storms <br />often result in increased accidents, falls, and injuries. The following categories represent the most <br />common and severe consequences for ice storms: <br />205 <br />