Thunderstorm Wind in Carroll County, Iowa

The airmass over Iowa was quite unstable during the predawn hours of the 10th with surface dew points in the 70s. In spite of the fact that a weak cold front had passed through the state, little drying of the atmosphere took place. An unseasonably strong upper level closed low pressure system moved southeast across North Dakota into west central Minnesota during the morning hours of the 10th. Several lines of thunderstorms formed over southeast South Dakota into northwest Iowa and moved southeast from there. The storms produced very heavy rainfall during the initial round of storms along with winds of 40 to 50 MPH. The thunderstorms formed into a well developed MCS by dawn with the second round of storms forming into a bow echo. Very high winds pushed from west central into central and parts of south central Iowa as the bow echo pushed southeast. Numerous reports of 60 to 70 MPH winds were received. Carroll County was especially hard hit with a 96 MPH wind gust recorded in Glidden. Carroll and Crawford Counties were the most heavily impacted. There were approximately 140 electrical transmission poles down in about a 4 mile stretch 2 miles north of Carroll and to the west. The loss of these lines disrupted large portions of western Carroll County, and eastern Crawford County. Newspaper reports received in early August indicated damage to the transmission lines at $1,500,000. The strongest winds, those exceeding 70 MPH, extended into Guthrie County. Winds in the Panora area topped out at 77 MPH. Extensive damage was reported to grain bins. One of the largest was in Guthrie County, where a 300,000 bushel bin was collapsed on one side by the winds. Crop damage in the area was into the millions of dollars. Survey results indicated that nearly 25% of the corn crop in Carroll County was totally flattened. Damage surveys also indicated very extensive crop damage on either side of Carroll County, in Crawford and Guthrie Counties as well as the north half of Audubon County. Governor Vilsack declared Carroll and Crawford Counties disaster areas. Early reports indicated damage to 70 to 80 percent of farm fields in both counties. Although no injuries were reported, high winds overturned a semi-tractortrailer truck in Madison County west of Winterset. The bow echo continued to move south-southeast across south central Iowa. The Lorimor area of Union County was hard hit. Tree Limbs and Power Lines down in Lorimor with 3 residences receiving minor damages from tree limbs. Two cars, a pickup, and camper were damaged by tree limbs in Lorimor. In rural Lorimor the top half of a large barn was gone along with the hay stored inside. Steel grain bins were damaged by flying debris and trees, and machinery was damage by sections of the building debris.