Flash Flooding and Hail in Iowa, June 23 to 24, 2000

Another round of convection developed over Iowa during the afternoon hours as warm and unstable air was drawn north over the top of the outflow boundary left behind from convection during the mid day hours. Very heavy rain fell along the arc of the outflow boundary. Severe weather was very limited with this event. One of the cells became severe over southwest Iowa over Cass County. The storm dropped one inch diameter hail on the town of Massena. This cell was the same cell the a short time earlier produced 70 MPH winds as it passed over Cumberland. The heavy rain was by far the dominant feature with this event. Precipitable water values were around two inches. The storms were in part enhanced by moisture streaming north from the remains of former Hurricane Carlotta. Heavy rainfall occurred over southwest Iowa as nearly six inches of rain fell in parts of Taylor County. Due to severe drought conditions in the area, no flash flooding occurred there. It was a different story farther to the east. Very heavy rainfall over Wapello, Monroe, Mahaska, Davis, and Marion Counties caused considerable flash flooding. A band of 6 to 12 inches of rain occurred along the Des Moines River between Ottumwa to northwest of Oskaloosa. Serious flash flooding took place over parts of southern Mahaska into Wapello County. At one point, 40 roads were reported under water and closed in Wapello County. The highest reported rainfall came from the Oskaloosa area, where an observer reported over 12 inches of rain, eight and one half of that fell in less than three hours. Other reports indicate four to eight inches of rain in Marion County, with three to five inches common in Wapello County. Reports indicate 4 to 5 inches of rain in Monroe County. Needless to say, many houses were flooded by the heavy rainfall. Crop damage was also quite widespread due to crops drowning in flooded fields. The situation would not have been as serious if not for the fact that 3 to 6 inches of rain fell across most of these areas about a week earlier.