Tornado and Flash Flooding in Iowa, June 12, 2001

The supercell that moved across northern Iowa during the early morning hours left behind a strong outflow boundary. This outflow boundary became established east to west across central Iowa. At the same time a complex of thunderstorms that was generated by a short wave moving across Nebraska advanced toward western Iowa just before sunrise. Though upper level jet divergence was in place, a strong mid level cap was in place through most of the night and the outflow boundary never produced any thunderstorm activity. Temperatures in the mid levels fall significantly around sunrise. The outflow boundary "lit up like a Christmas tree" around sunrise. The thunderstorms became severe quickly and were large hail producers. The storms moved east along the east to west line and also produced copious amounts of rainfall. Initially the threat was the large hail. Numerous reports of one to two inch diameter hail were received through central Iowa. Some of the greatest damage occurred in the Des Moines metropolitan area as golf ball size hail pelted the city. Damage was significant to both roofs as well as cars. Several large car dealerships were hit on the west side of town with significant damage reported. Estimates of damage were in the area of $250,000 to $500,000 each. One off duty NWS employee on the west side has his back window broken out by hail with numerous hail pocks in the car. Initial estimates of damage on the west side of town indicate about 5000 insurance claims for cars at $900 to $1500 each, plus 3000 insurance claims for damages house roofs. Golf ball size hail and 4 inches of rain fell near Grinnell in Poweshiek County. Hail drifted to a depth of 2 to 3 feet deep in places. Crops were totally destroyed as the hail fell for 25 minutes. One farmer in the area reported 1000 acres of crops destroyed. Wind was not a major factor with most of these storms. One high wind report was received in Jasper County south of Prairie City. Several trees were blown down there. In addition, one tornado touched down briefly in the county. The touchdown was in open country west of the town of Montezuma. The tornado did little damage and lifted in a very short time. Focus then shifted to the heavy rainfall. The storms trained along the east west line for several hours. A band of very heavy rain was reported from Greene County, east into Boone, Story, Dallas, and Polk Counties. Rainfall of three to four inches was common in these areas. Numerous roads were closed due to the high water. Water was standing in fields everywhere. Some of the worst damage occurred in Story County as the densely populated area of Ames and Iowa State University was affected. By the mid afternoon hours, the thunderstorms weakened and began to lift north slowly. During the early afternoon hours as the thunderstorms moved through Sac County, lightning struck a tree in the town of Schaller. The tree was split and landed on the house causing several thousand dollars damage.