National Weather Service United States Department of Commerce

Overview

Very heavy rain on Saturday and Sunday, June 7-8th 2008, resulted in record flooding across a large portion of the region, along with a few bouts of hail, damaging winds, and tornadoes.

A warm front ran west to east across the Upper Mississippi River Valley on Saturday the 7th, providing the focus for shower and thunderstorm development. A very moist and unstable airmass surged northward into and across this boundary, setting the stage for not only a severe weather threat, but for a high risk of heavy rain.

On Saturday the 7th, a significant return of moisture and warmth during the overnight hours Friday led to the development of a cluster of thunderstorms which moved out of southern Minnesota into western Wisconsin Saturday morning. These storms posed a small hail risk, with rainfall amounts around an inch as they moved along and north of the Interstate 90 corridor through noon. During the early afternoon hours on Saturday, the remnants of these storms encountered greater instability as warmth and moisture continued to feed into the area on a very strong southerly flow over Iowa. A severe thunderstorm developed over Monroe county early in the afternoon, and moved east along Interstate 90 with an attendant threat of tornadoes, damaging winds, and large hail. This was the first of what would be numerous supercell thunderstorms which then developed over much of the area of south of Interstate 90 through the rest of the afternoon into the early evening. All of these storms exhibited strong circulations on radar, with numerous reports of rotating wall clouds, funnel clouds, and brief tornadoes. Given the extreme amounts of moisture, these storms also exhibited a very high rainfall rate, which led to 1 to 2 inch rainfall amounts in an hour or so. As these storms congealed into a larger scale line of thunderstorms, the repeat (or training) of these storms led to flash flooding conditions through the evening and overnight.

For further information on the tornadoes, read the tornado summary for that day.

On Sunday the 8th, the warm front was lingering across the region, but a cold front was quickly tracking east 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, while a few storms produced damaging winds. The severe weather activity, aside from the heavy rain, was much less locally compared to Saturday.

The Sunday rainfall exasperated the already  dangerous flooding conditions across parts of southeast Minnesota, northeast Iowa, and southwest into central Wisconsin. Many roads were already closed from the Saturday rain due to water over the roadways, mudslides, or partial washouts. The Sunday rains worsened the conditions, leading to more road closures, sandbagging, and some evacuations.

While the rain was tapering off and moving east Sunday night, 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.

Image
Bridge destroyed on County Road W42 between Clermont and Eldorado, IA from June 8, 2008 flooding
nws logo Media use of NWS Web News Stories is encouraged!
Please acknowledge the NWS as the source of any news information accessed from this site.
nws logo