Damaging Wind in Iowa, August 16, 1997

A very unstable atmosphere was in place over Iowa as a strong cold front approached from the northwest. Surface dew point temperatures were in the mid to upper 70s with 850 mb dew points in the upper teens Celcius. CAPE values were near 5000 J/kg and in some instances near 8000 J/kg. Thunderstorms were slow to fire, but once they did development was explosive. Thunderstorms formed into a mesoscale convective complex (MCC) during the evening hours. As it typical of MCC development, severe weather occurred during the first few hours of it's development. Large hail occurred south of Des Moines, just south of Indianola with up to golf ball size hail measured. This was the largest hail reported, however many areas received up to marble size hail. At least two small tornadoes touched down early on in the storms development. These were both quite weak and only touched down intermittently. One was over the far south central part of Warren County, the second just south of Indianola. Fortunately, both of these tornadoes were in open country and caused little damage beyond crop damage. During the mid evening hours, winds became a problem over southeast Iowa. Sixty MPH winds were reported in Ottumwa, resulting in some damage around the city. The storms did produce significant rainfall. Three to six inches of rain fell over portions of Marion, Lucas, and Wayne Counties. Reports from the area indicate some ponding of water, however no significant flooding occurred due to the dry andicedent soil conditions.