Flash Flood — Waukesha, Wisconsin

2025-08-10 · near Merton, Waukesha, Wisconsin

Event narrative

Some flash flooding of streets, creeks, and low lying neighborhoods in Merton, Hartland, Delafield, Oconomowoc and surrounding areas.

Wider weather episode

A historic flash flood and record rainfall occurred over portions of the Milwaukee Metropolitan Area and Southeast WI resulting in damages in the $100s Millions. Warm, moist, and unstable air rose along a stalled front to produce numerous thunderstorms and more than 10 inches of rain in many locations. Widespread flash flooding of streets, creeks, rivers, and low lying neighborhoods occurred. A homeless camp in Milwaukee underneath 1st Street Bridge adjacent to the surge of record flooding on the Kinnickinnic River was swept away. One or two deaths may be a result of this flash flooding with a couple others missing. Thousands of residential homes or businesses sustained major flood damage with dozens classified as destroyed due to 1st floor flooding, basement flooding or foundation collapse. Residential sewage backups, and raw sewage released into rivers and Lake MI by many municipalities was common. A small number of complete road washouts and swift water rescues occurred, in addition to dozens of people stranded in their vehicles in deep, still water in low lying areas. First responders had difficulty getting to their 911 calls including stranded motorists and flooded neighborhoods, due to the numerous flooded roads. Dozens of people were evacuated or relocated from their flooded homes and neighborhoods. Longer duration areal flooding and river flooding, which ranged from moderate flooding to record flooding, then continued for a couple more days. In addition to the flash flooding, a couple hikers were struck by lightning, via a ground current from a nearby strike on a tree, on the Ice Age Trail near Palmyra. They were initially rendered unconscious but did survive.

View location on OpenStreetMap → (43.1606, -88.2878)

Source: NOAA Storm Events Database, event_id 1281063. Narrative written by the NWS forecast office that issued the report.