Resolution 7478 hazard mitigation

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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan Volume 2 — Hazard Inventory July 23-24,1987, Super Storm The heaviest rainfall ever officially recorded at a Twin Cities weather station fell between about 18:00 CDT on 23 July and about 02:00 CDT on 24 July 1987. During this eight -hour interval, observers at the Twin Cities International airport station measured an even ten inches of rain (9.15 inches of which fell in a five -hour period). In addition to the heavy rainfall, the 23-24 July storm spawned an F3 tornado near Goose Lake in Hennepin County and produced extensive damage in Maple Grove and Brooklyn Park. Damage in other areas was extensive, largely the result of flooded homes and businesses, ruptured storm sewers, and washed out or inundated streets and highways. Two flood related deaths were reported, and property damage was estimated to be in excess of $30 million (1987 dollars). The 23-24 July storms occurred along an outflow boundary that had separated extremely warm, moist air to the south and east and much cooler, drier air immediately to the north and west. The interaction of these air masses produced intense thunderstorms with extremely heavy rainfall over the southwestern portion of the Twin Cities on 20-21 July 1987, two days prior to the 23-24 July outbreak. Rainfall amounts during this event included 3.83 inches at the Twin Cities airport station, 9.75 inches near Shakopee and 7.83 inches at the neighboring community of Chaska. The 23-24 and 20-21 July storms, together with the rainfall produced by thunderstorms earlier and later in the month, brought unprecedented July rainfall to the Twin Cities area. The International airport station recorded 17.91 inches, approximately six times the July normal. An unofficial monthly total of 19.27 inches was recorded in west Bloomington. Ironically, July 1987's excessive rainfall came in the middle of a prolonged period of subnormal precipitation. Precipitation had been below normal for every month from October 1986 through June 1987 and, following about six weeks of wet weather in July -August 1987, the drought returned. Extreme dryness prevailed during much of the ensuing year with a near record dry June and record warmth during the summer of 1988. July 1,1997, Derecho and Flood An intense mesoscale system containing supercells and a fast-moving squall line tore through the central and northern Twin Cities area during the evening, producing extensive wind damage and catastrophic flooding. Numerous tornadoes rated up to F3, were reported from the Willmar area, through Wright and Sherburne Counties. Non-tornadic winds more than 100 mph knocked out power, severely damaged structures, and snapped and uprooted trees in Wright, Anoka, Sherburne, and northern Hennepin counties. As the storm complex moved into the central portions of the Twin Cities, it produced some of the heaviest one -hour rainfall ever measured in Minnesota. 3-4 inches fell within one hour over the central and eastern parts of Hennepin County, as well as adjacent portions of Ramsey and Anoka counties. 1-35 and 1-94 were closed south of downtown Minneapolis and standing water more than 10 feet in some areas prompted boat rescues in south Minneapolis and Richfield. Edison High School in northeast Minneapolis sustained major flood damage, and hundreds of homes and residential complexes were severely damaged by inundation. 122