Tornado and Hail in Iowa, September 7, 1999

The seasons first dynamic cold front moved southeast into Iowa during the evening hours of the 7th. Temperatures warmed rapidly during the day on a gusty south wind. Readings topped out in the mid 80s to low 90s across the state. Dew point temperatures climbed into the mid 60s to low 70s across the region by the late afternoon. These conditions combined to produce surface based CAPE values of 3500 to 4500 J/kg ahead of the front. A narrow line of thunderstorms developed just ahead of the cold front during the late afternoon hours. The environment became favourable for severe thunderstorm development as mid level winds were increasing and had increased to 50 to 60 kts before sunset. The storms became severe and produced hail at several locations from north central into southwest Iowa. The largest hail was golf ball in size and fell in the north central part of the state. Gusty winds were also common with the storms, though most of the storms only produced winds around 50 MPH. One of the storms produced very high winds in Webster County from what appeared to be a downburst. Winds around 90 MPH flattened crops in a 5 square mile area. One farmstead was hit with damage reported there including a grain dryer toppled. In addition, a grain dryer was toppled at the cooperative, costing between $300,000 and $400,000. The storms weakened a few hours after sunset with no severe weather reported by the late evening hours. During the early evening as the line of storms moved through southwest Iowa, hail nearly golf ball in size fell in Adams County. A tornado touched down in Taylor County, briefly, northwest of Gravity. The only damage was crop damage as it was over open country.