Flooding in Iowa, July 2 to 7, 1999

In years to come, July 1999 will be remembered in northeast Iowa for the "Floods of '99". Record to near record river flooding affected much of this area through the month. Within the Des Moines HSA, the major rivers most affected were the Cedar, Shell Rock, and Beaver Creek. However, numerous tributaries and smaller streams saw severe flooding and flash flooding due to repeat heavy rainfall events. Much of the month featured strong ridging both surface and aloft anchored over the southeastern U.S. and an anomalously deep trough over the western U.S. This pattern was conducive to the creation of a major drought over the eastern states, but lead to very heavy rain over northern iowa. Southern Iowa had a month more typical of the drought areas, with well below normal rains. Northeastern Iowa became a favored area for mesoscale convective system formation, as very warm, humid air was repeatedly drawn into slow-moving boundaries with resultant torrential rains. The first major event to affect the area was during the afternoon and nighttime hours of July 2. What began as a severe weather event ended up as a flooding rainfall in northeast Iowa. The heaviest rains fell in a tight east to west band, widening to the east, through the extreme southern parts of Franklin, Butler, and Floyd Counties and the extreme northern parts of Hardin, Grundy, and Black Hawk Counties. Initially, flash flood warnings were issued for parts of these counties. WSR-88D estimates of 5 to 8 inches of rain fell in these areas in only a few hours. Parkersburg, in southern Butler County, measured 6.55 inches of rain in a 24 hour period, although most of it fell in a much shorter time. Waterloo picked up 5.60 inches for the 24 hours. The result was widespread flooding and flash flooding. According to FEMA, over 2500 homes were damaged in four counties, all of which received a Presidential Disaster Declaration made on July 22. Butler and Black Hawk Counties in the Des Moines HSA were both part of the this disaster declaration. Flooding was extensive along Beaver Creek, primarily affecting the town of New Hartford. The creek reached the 5th highest crest of record on the 3rd. Due to the limited areal extent of the rains, there was little river flooding outside of the Beaver Creek basin. Also with this event, the only flooding of significance to affect central Iowa also took place. The flooding took place along the Raccoon River as a result of heavy rains from the same system. The river near Van Meter crested slightly above flood stage late on the 3rd. The passage of an active cold front which dropped 1 to 3 inches of rain, caused another minor flooding event along the mainstem Raccoon on the 6th as Van Meter crested a little over three quarters of a foot above flood stage. The Raccoon River in Des Moines did not reach flood stage from either of these events, but rather crested just below flood stage.