Damaging Wind in Iowa, June 21, 1997

An extremely unstable air mass was over Iowa during the afternoon and evening of the 20th. Lifted indices were near -15 degrees C. with CAPE values of 4000 to 6000 J/kg. A weak frontal boundary was draped across the northern part of the state. Thunderstorms erupted along this boundary after sunset and became severe quickly. The air mass was quite warm with freezing levels between 14,000 and 15,000 feet. This kept the hail size down across the state. Fairly early in the storm systems evolution, high winds hit Webster County. A barn was downed near the town of Badger, trapping two people inside. Each reported minor injuries. A car was also destroyed inside the barn and the barn was moved off of its foundation. Heavy rainfall was a problem over the west central, north central, and northeast counties where up to 6 inches of rain fell from the line of storms. Flooding became a problem the next day in spite of the dry conditions that existed prior to the rainfall. During the later evening, the storms began taking on a bow echo appearance. There were two areas where bow echos formed. One was over the northeast, the other moved across southwest, into central, south central, and southeast Iowa. These produced very high winds in the 70 to 100 MPH range. Some of the worst damage occurred just southwest Waterloo. In Butler County, high winds downed and split a silo in half. Another was moved 50 feet off its foundation. Winds in the area were in excess of 90 MPH. A second bow echo swept across the southern part of the state. It produced high winds all the way across the state as it did. Significant damage was reported over western IOwa. South of cumberland a 300,000 bushel grain bin was destroyed with it's contents a total loss. The worst damage occurred in Marion County around Knoxville. Winds near 100 MPH caused considerable damage to the city. High winds in Hartford, in Warren County, snapped off 100 foot trees. Some Oak trees 2 to 3 feet in diameter were snapped off by the winds. WSR-88D velocity products indicated a 108 MPH wind over the area at this time. Govenor Branstad declared a State disaster in Marion County following the damage. It was considered so extensive across the county, this enabled assistence in cleanup. As mentioned, hail was not a major problem. Golf ball size hail was reported near the beginning of the storm systems development. At that time, WSR-88D VIL values were 95 Kg/m/m. Extensive crop damage occurred north and east of Eagle Grove. It was reported the hail stripped a 3-4 x 7-8 mile area. Though not totally destroyed, damage was extensive.