Flooding in Iowa, July 10 to 15, 2000

A major flash flood event began during the evening hours of July 9, as a large mesoscale convective system developed over northern Iowa and moved slowly southeast. The event was well anticipated by the NWS, as a Flood Potential Statement for the Cedar River Basin and Flash Flood Watch were issued around noon on the 9th. The watch covered the northern one half of Iowa. Ingredients in place over this area included a very moist and unstable airmass, a nearly stationary frontal boundary, a strong low-level jet, and a series of short-waves moving into the upper ridge in place over the region. Storms developed explosively during the late evening hours of the 9th, with Flash Flood Warnings issued in rapid succession for Emmet, Palo Alta, Kossuth, and Humboldt Counties. Rainfall rates of 1 to 3 inches were observed with many of these storms, and numerous reports of flooding received by the NWS. During the early morning hours of the 10th additional Flash Flood Warnings were issued for Cerro Gordo, Worth, Wright, and finally a blanket Flash Flood Warning for Grundy, Hardin, Butler, Franklin, Black Hawk, and Bremer Counties. by daylight on the 10th, the most serious flooding appeared to be over extreme southern Kossuth and northern Humboldt Counties. Numerous roads were closed or washed out in this area. The towns of LuVerne and Livermore were especially hard hit. Rain gage reports were sparse, although an unofficial report of 6 inches in LuVerne, in extreme southern Kossuth County, was reported. Doppler radar estimated that 6 to 8 inches and possibly an isolated 10 inch amount fell over this area. Heavy rains also fell early on the 10th over parts of Tama County, with numerous roads closed and estimates of 5 to 6 inches of rain. As the Flash Flood Warnings expired, Countywide Flood Warnings were issued for northern Humboldt, southern Kossuth, northern Tama, Grundy, and Black Hawk Counties. Surprisingly, there was only minor river flooding from all this precipitation. The rains in the upper Des Moines basin fell over an area that had been in drought much of the spring and early summer. The East Fork Des Moines River at Algona rose very close to flood stage in response to the heavy rains on the 9th and 10th, but the most extreme rains fell south of this location. There was some minor river flooding along the Cedar River, mainly at Janesville and Waterloo on the 13th and 14th, and also along the Beaver Creek at New Hartford.