Resolution 7478 hazard mitigation

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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan Volume 2 — Hazard Inventory Phase 1 Phase 2 Phase 3 Non -hazardous "°"011llllll Non -hazardous weather lulu weather IIIII The four generalized scenarios in which non -convective extreme winds most frequently occur in the Upper Midwest. It should be noted that a single system may produce different scenarios at different locations. The Armistice Day storm 1940 generated each of the four scenarios listed. Considering that thunderstorm hazards tend to be distributed in the southeast quadrant of a cyclone, that blizzards tend to occupy the northwestern quadrant, and that any system capable of both will tend to move northeastward through the region, it is unlikely that any given location will experience severe thunderstorms, non -convective extreme winds, and blizzard conditions from the same system. However, a powerful system on November 11, 1911, did just that, producing killer tornadoes in Iowa, Wisconsin, Illinois, and Missouri, followed by record -setting temperature drops of 60-80 degrees in 6-10 hours with blizzard conditions and wind gusts as high as 75 mph. This event is a true singularity in the central US, in that nothing else like it has ever been recorded. Perhaps the most common scenario for any one location in the Upper Midwest is that the extreme winds follow a period of inclement but otherwise non -hazardous weather and are followed by a return to non- hazardous weather as well. The scenario a given event follows is determined by both relative position with respect to the center of low pressure, and the depth of cold and/or warm air and moisture available to the system as it moves through the region. Those factors, in turn, influence the likelihood of cascading effects. In Scenario 1, the primary impacts are damage and power outages, and weather conditions in the storm's wake generally will not further escalate the situation. In all other scenarios, there is some potential for combinations of the following cascading effects. Severe weather — Virtually all known non -convective extreme wind -producing systems in the Upper Midwest have also produced severe weather hazards somewhere within the storm's warm sector, which is in its southeast quadrant. Incidentally, concentrations of a system's most extreme non -convective winds typically follow the cold front into the southeast quadrant as well. Thus, if a sufficiently intense system produces tornadoes or straight-line winds (both of which can form in the high -shear environments of these systems if enough instability is present), some of the 189