A line of thunderstorms moved across southern Wisconsin Friday morning. Scattered thunderstorms Friday evening evolved into a line of thunderstorms oriented west to east through southern Wisconsin early Saturday morning. This line of thunderstorms remained stationary in portions of south central Wisconsin and brought 4-8 inches of rain to Iowa, northeast Lafayette, northwest Green, and far southwest Dane counties by mid morning. Saturday evening, another round of storms pushed across southwest and south-central Wisconsin dropping another 2 to 4 inches over the areas hardest hit earlier that morning. Rainfall totals from Friday morning through Monday morning are shown in the image below.
The heavy downpours flooded roads, created a sinkhole, and washed out a few roads in southwest and south central Wisconsin. Many rivers are over their banks or experiencing minor flooding.
This wet pattern was a result of strong low level flow which brought very moist air up from the Gulf of Mexico. The upper Midwest was a target for thunderstorms due to the hot and moist airmass in place and strong winds aloft. A frontal boundary draped across the Minnesota/Iowa border and southern Wisconsin helped focus the storms across the region. Heavy rain occurred along this boundary and created flooding in southeast Minnesota, eastern Iowa, and northwest Illinois, as well as southwest and south-central Wisconsin.
National Weather Service Milwaukee/Sullivan