Flash Flood — Allamakee, Iowa

2008-06-07 · near Quandahl, Allamakee, Iowa

Event narrative

Excessive rainfall caused fairly widespread flash flooding across the county. Steep terrain enhanced the flash flood threat causing mud slides and damaged infrastructure. Numerous roads were washed out and bridges damaged. A mud slide at Camp Tahigwa Girl Scout camp near Dorchester trapped part of the staff, but no one was injured. In Dorchester, the Waterloo Creek flash flooded swamping several mobile homes or trailers and cars along Highway 76. Water swept through town very quickly trapping people on their cars and roof tops. There were three injuries as a result.

Wider weather episode

A warm front extended east to west across the Upper Mississippi Valley on June 7, which provided the focus for thunderstorms producing excessive rainfall. In fact, these storms exhibited very high rainfall rates, which led to 1 to 2 inch rainfall amounts in an hour. As the storms congealed into a larger scale line of thunderstorms, they continued to move over the same areas, which led to significant flash flooding through the evening and overnight.

On June 8, the warm front was lingering across the region, but a cold front approached out of the northern Plains. Showers and storms would redevelop during the day in the vicinity of the warm front, while a line of storms developed out ahead of the cold front, with these tracking across the region Sunday night. Again, copious amounts of moisture lead to periods of heavy rain.

The heavy rainfall on June 8 enhanced the already dangerous flooding conditions across parts of northeast Iowa. Many roads were already closed from the June 7 rains due to water over the roadways, mudslides, or partial washouts. Conditions only worsened, leading to more road closures, sandbagging, and some evacuations.

While the rain was tapering off and moving east Sunday night, June 8, the rivers continued to rise, and some extremely quickly. Some rivers responded with a foot per hour rises, while others eventually exceeded their river gauges ability to record the river levels. These gauges were under water themselves! All-time record crests were set at a few locations, with top 5 records at many others.

Damage to infrastructure and crops was preliminarily estimated at 70 to 80 million dollars. As a result, Mitchell, Floyd, Howard, Chickasaw, Winneshiek, Fayette, Allamakee and Clayton Counties were all declared federal disaster areas.

View location on OpenStreetMap → (43.4908, -91.7001)

Source: NOAA Storm Events Database, event_id 112019. Narrative written by the NWS forecast office that issued the report.