High Wind in Black Hawk, Iowa

Significant wind damage occurred in Dunkerton, where a COOP was damaged.

The seasons first strong push of cold air moved south into the central U.S. on the 26th. A very strong upper level trough of low pressure aloft dropped south out of Saskatchewan accompanied by a strong upper level jet stream and a tropospheric fold. As the cold air moved in, the atmosphere became adiabatic, creating a mixed layer, up to the 700 mb to 600 mb level. The mixed layer contained very strong winds of 60 to 70 kts. The downward momentum in the subsidence area behind a cold front that moved south across the area produced high winds over a large part of the state. Most areas reported sustained winds of 40 to 45 MPH for several hours, with many areas reporting gusts of 60 to 65 MPH. The highest gust was recorded in Polk County in West Des Moines with a gust of 69 MPH. Some of the other higher gusts occurred in north central Iowa with a 68 MPH wind gust in Cerro Gordo County at Ventura, and in Polk County in Windsor Heights. Scattered damage was reported around the state with numerous tree branches broken and some trees blown over. Power was knocked out in several locations. In the Des Moines metropolitan area, about 17,000 homes were without power at the height of the storm. Power was out for 3 to 6 hours in most cases. Thousands of homes were without power for brief periods of time during the wind event. In Black Hawk County, at Dunkerton, the high winds caused severe damage to a nearly completed new COOP with damage estimated over a million dollars. The new COOP was under construction following the damage earlier in the spring as a tornado destroyed the old one. There was some crop damage as well as the high winds caused lodging of some of the corn around the state as the harvest was not yet complete. During the afternoon of the 26th, the high winds caused some travel problems as it was difficult to maintain control due to cross winds. The mile long bridge across the Saylorville Reservoir near Polk City, in Polk County, was closed for several hours due to the high winds for safety reasons.