Tornadoes and Flash Flooding in Iowa, June 8 to 9, 1999

A strong upper level disturbance moved north-northeast into Iowa during the afternoon hours. A very unstable airmass was in place over the state with lifted indices near -10 degrees C. Surface dew points were in the low 70s as high temperatures soared into the upper 80s and 90s. This combined to produce CAPE values near 5000 J/kg. Thunderstorms erupted initially developed in more or less an east to west line. That line lifted north and as it did produced very heavy rain and some hail of three quarters of an inch to an inch in diameter. A second line formed in a more north to south orientation and moved east across the state. There were also some reports of dime size or larger hail from that line as well. Serious crop damage occurred in Hancock County southeast of Kanawha due to the hail. Crops needed to be replanted in the area. The main problem was with the intersection of the two lines. At the intersection of the two outflow boundaries from the lines a few brief tornadoes occurred. These were more like spin up tornadoes and were very short lived, causing no significant damage. One was in Wright County north of Goldfield, another Humboldt County southwest of Renwick, with yet another in Hancock County southeast of the Kanawha area. As the storms moved through the Lake Mills area in Winnebago County, high winds downed trees and caused vehicle damage. As the evening progressed, the upper level vorticity maximum was evident in the radar signature. The comma head of the precipitation passes over Black Hawk and Grundy Counties. Reports southeast of Waterloo indicated 3.76 inches of rainfall in a 90 minute period. Meanwhile, the area between Reinbeck and Wellsburg received in excess of 5 inches of rain in a 3 hour period. Normally, this amount of rain would not be all that serious, however soil conditions in that part of the state were very saturated resulting in significant runoff. Flash flooding occurred in the two counties. Numerous gravel roads were washed out over the northwest part of Butler County with widespread flooding reported between Reinbeck and Wellsburg.