Resolution 7478 hazard mitigation

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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan Volume 2 — Hazard Inventory 4.3.9.7. Historical Data Bld The "Dust Bowl" era of the 1930s was so named because of massive dust storms that frequently ravaged the Plains during that extraordinarily dry period. During this period, Minnesota saw some of the worst dust storms in its history. In 1934, dry conditions combined with high winds to produce thick dust on five or more dates at the end of the month. February had at least six more dust storm dates, followed by 15 dates in March, and 19 dates in April, with the worst of the dust storms occurring on May 9-10. Meteorologists at the time reported these latter dust storms were likely the most severe of their kind ever experienced in the area, with extreme soil erosion exposing and subjecting new seed to the strong winds. The most recent severe dust storm clipped western Minnesota and hit much of South Dakota head-on during a severe weather outbreak on May 12, 2022. Intense downburst winds generated by severe thunderstorms advanced well ahead of the storms at speeds of 60-80 mph. The region had been quite dry, and soils were loose and unprotected by vegetation. As a result, a huge cloud of thick dust raced north northeastward across the region, dropping visibilities to zero in spots, especially in Nebraska and South Dakota. Visibility below a quarter mile was common in western Minnesota. A lighter cloud of blowing dust moved into Hennepin County during the evening, though visibility was hardly reduced, and no impacts were reported. There have been no other incidents that are within the scope of this plan. 4.3.9.8. Future Trends Ble There is no current research available on the direct effects of future climate conditions on the incidence of dust storms. However, because drought conditions have the effect of reducing wetlands and drying soils, droughts can increase the amount of soil particulate matter available to be entrained in high winds, where agriculture practices include tilling. This correlation between drought conditions and dust storms means that an increase in future droughts could increase the incidence of dust storms, even though the drought is not directly related to the directly to the dust storm. 4.3.9.9. Indications and Forecasting Dust storms move quickly. Other than seeing a wall of brown dust approaching in the distance, there is not much warning before a dust storm arrives. However, they usually precede thunderstorms. So if conditions have been dry, and one can see a large cumulonimbus cloud and feel the wind is picking up, one can expect dust to be blowing with the possibility of dust storm type reduced visibilities and consequences. Dust storm events are caused by different weather systems showing different intensities and identifiable characterizes in observational systems. There are four dust storm generation types: frontal, meso- or small-scale, disturbances, and cyclogenesis. Key features of cold front -induced dust storms are their rapid process with strong dust emissions and a large, affected area. Frontal dust storms typically last 3-5 hours with wind speeds of 36-83 mph and typically affect an area of 7,700 to 77,000 square miles. Meso- or small-scale dust storms are the most common type of dust storm including thunderstorms, convections along dry lines, gusty winds cause by high pressure, and more. The most common occurrence are thunderstorms in which the organized outflow from the downdrafts of decaying thunderstorms blows 156