A warm front extended west to east across the Upper Mississippi River Valley on June 7, which provided the focus for thunderstorms producing excessive rainfall and other severe weather. In fact, these storms exhibited very high rainfall rates, which led to 1 to 2 inch rainfall amounts in an hour or so. 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, this same warm front lingered across the region, but a cold front approached from 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 southwest Wisconsin. 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 75 to 85 million dollars. As a result, Crawford, Grant, Juneau, Monroe, Richland and Vernon Counties in central and southwest Wisconsin were declared federal disaster areas.