Flood and Hail in Iowa, September 11, 2000

Ingredients were present for a big outbreak of severe weather. A strong upper level disturbance was moving through the plains. Meanwhile, surface low pressure raced from Southwest Minnesota into Wisconsin by late afternoon, allowing a strong cold front to sweep into Central Iowa by late in the day. Ahead of the front, a strong southwest breeze and abundant sunshine pushed temperatures to record levels with readings generally in the mid and upper 90s. An old outflow boundary from earlier convection set up over Northeast Iowa and Northern Illinois. Thunderstorms redeveloped along the boundary by mid to late afternoon over Northeast Iowa and quickly became severe. The convection took on an east to west orientation, which resulted in training of cells leading to heavy rains in excess of 3 inches, and recurring reports of severe weather. Meanwhile, thunderstorms exploded late in the afternoon along the approaching cold front from near Des Moines, Iowa to St. Joseph, Missouri. Strong convective instability and strengthening vertical wind shear profiles resulted in the formation of an intense squall line. The squall line raced eastward producing numerous reports of large hail and damaging winds. By the time the squall line reached the Quad Cities, the old outflow boundary over Northeast Iowa and Northern Illinois had sagged south and extended from near Moline, Illinois to Lafayette, Indiana. A combination of the boundary and increasing westerly component to the mid level winds with the approaching disturbance, enhanced a segment of the squall line over portions of the Quad Cities, evolving into a bow echo. Winds estimated in excess of 70 mph at times battered much of the Iowa Quad Cities. The cities of Bettendorf, Pleasant Valley, Riverdale and Davenport were hit hardest with numerous trees and power lines knocked down. The Illinois Quad Cities avoided the brunt of the storm. 28,000 homes were without power in the Quad Cities, and many did not have power restored for days. Many other areas in Eastern Iowa lost power as well. The lack of power forced the cancellation of classes at Scott Community College. The storms also did considerable damage to many of the areas corn and soybean crops. Damage was widespread but variable, with as much as 10 percent of the corn crop damaged in some areas. Several factors contributed to the damage. A big factor was the direction of the rows in relation to the wind. Other factors included the variety of corn, as some were not rooted as deeply, and stalk rot which makes corn stalks brittle and unstable. Stalk rot was brought on by a wet July and relatively dry August.