Tornado and Flash Flooding in Iowa, June 25 to 26, 2000

A major wind and significant flash flooding event took shape across Iowa during the afternoon and evening of the 25th. A dynamic upper level system approached Iowa from the northwest during the afternoon. Several boundaries were in the area resulting from weak convection that took place during the morning. Very strong theta-e advection took place over northeast Nebraska during the morning and early afternoon hours. In addition, several other factors came into play. Moisture continued to stream into Iowa from the remnants of Hurricane Carlotta as precipitable water values approached 2.2 inches. Iowa was also under the influence of a coupled jet structure. As a result a strong upper level divergent field was in place over the state. By afternoon, mid and upper level cold air advection began to take place as well. Strong convection took place by mid day over northeast Nebraska into west central Iowa. The line of thunderstorms moved into rich air with surface dew points in the low to mid 70s. The main feature with the storms was high winds. The line of thunderstorms took on a bow echo configuration as it moved across southern Iowa. Most of the southern three tiers of counties reported high winds. Wind speeds of 60 to as much as 85 MPH were reported with the storms. Wind speeds topped out at 85 MPH at New Virginia, in Warren County. Damage was widespread with numerous trees and power lines downed by the winds. Some trees up to 2 feet in diameter were snapped. A flag pole was reported bent 4 inches by the high winds as well. One tornado was reported in Warren County as well. This was a brief tornado near St Marys which caused no damage. The other problem with the storms was the heavy rainfall. Two to three inches of rain fell in many areas. As the storms moved into parts of south central and southeast Iowa, they moved into area that had been inundated by heavy rainfall just two nights before. Flash flooding was reported in Appanoose, Lucas, Mahaska, Monroe, Wayne, Davis, and Wapello Counties. Numerous roads were under water in these counties. U.S. Highway 63 was closed by high water north of Ottumwa. Some of the worst flooding took place in Mahaska County where heavy rain fell on areas that had been flooded two days before. At least 15 roads were reported under water in the county. As the thunderstorms moved through Hamilton County, lightning struck a tree outside of a house in Stratford. It also left a hole in the ground and caused damage inside the house. The lightning strike broke windows out of the front of the house and also caused windows to break in the house next door. Later, the storms moved into the Waterloo area. Lightning struck the chimney of a former school building. The top part of the chimney was blown off by the lightning and a good part of the rest of the chimney was damaged.