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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />Occupants of cars and trucks also are vulnerable to being hit by falling trees and utility poles. Further, high <br />profile vehicles such as semi -trailer trucks, buses, and sport utility vehicles are frequently blown over <br />during sustained non -convective wind events. <br />Though they only make up 5% of the 1980-2005 deaths shown above, construction sites may make larger <br />proportional contributions during periods of high economic growth, when the number of large projects <br />multiplies. Workers have been and can be blown from ledges or scaffolding and bombarded by loose <br />materials. <br />Because they are so rare, the Twin Cities area has not experienced the consequences of a major non - <br />convective wind event in several decades. Examination of the event in 1949, combined with what is known <br />about derechos, suggests that a current -era repeat would be catastrophic. The total population exposed — <br />outdoors, on the streets, in traffic —would likely be several times larger than in 1949. Power disruptions <br />would cover the entire metropolitan area, and thousands of roads and street segments would be blocked <br />by fallen trees, wires, and utility poles. The breadth of an extreme system, acting on our complex and <br />dense concentration of overhead distribution feeders, would necessitate a massive temporary workforce <br />to restore service after an event. Outages would likely last days, which could be particularly dangerous if <br />winter conditions followed the high winds. <br />4.3.12.4. Potential for Cascading Effects <br />Non -convective high winds can occupy a large portion of any strong extratropical cyclone, and as a result <br />can follow, precede, or be accompanied by a wide range of weather conditions. The parent intense low- <br />pressure systems frequently produce severe thunderstorms and tornadoes in areas that are later affected <br />by the non -convective high or extreme winds. In some cases, the dangerous winds stretch far <br />northwestward, into the portion of the cyclone where heavy snow is falling or has fallen. In these <br />situations, severe blizzard conditions develop, and the winds function as one of many mutually enhancing <br />hazards. <br />188 <br />