Flash Flood in Waukesha County, Wisconsin

Thunderstorms training over the region produced 4 to 7 inches of rain over Waukesha County. While many sections of the county experienced flash flooding, the north and northeast sections were hardest hit, with numerous roads flooded and basements flooded in Brookfield, Menomonee Falls and Sussex. A trained spotter reported 4 inches of rain in one hour in Menomonee Falls where the heavy rains caused a sink hole to form on Campbell Drive. Rushing water flooded roads in Delafield near U.S. Highway 18, closed STH 59 at STH 164 south of Waukesha, and covered sections of CTH Z, west of Eagle in western Waukesha County. Flooded roads were also reported in Muskego, New Berlin and Oconomowoc.

Parts of south-central and southeast Wisconsin experienced several rounds of record-setting torrential heavy rains during the afternoon and evening hours of July 22, 2010 that led to flash flooding and damage. During the afternoon, a persistent band of strong to severe thunderstorms developed and moved very slowly over south central and southeast Wisconsin through the evening hours. The individual storms were moving quite fast, about 40 to 50 mph, but the slow southward movement of the boundary these storms were developing along, resulted in storms repeatedly training, or moving, over the same area.

Widespread 3 to 4 inch amounts were reported along and either side of the I-94 corridor, with locally higher amounts of 5 to 8 inches. The greatest rain amounts fell in Milwaukee County. Mitchell Field recorded 5.61 inches for the day, breaking a record for the date. The previous record was 1.26 set in 1948. This also is the second highest daily rainfall total on record for Milwaukee. The greatest one-day precipitation record was the 6.81 inches which fell on August 6, 1986. Madison also set a record for precipitation for the date at 3.62 inches. This beat the previous mark of 2.21 inches set in 1885. The 3.62 inches of rainfall ranks 13th for the most precipitation received in one day. The record is the 4.96 inches which fell on August 8, 1906.

About 32,000 We Energy utility customers lost electrical power throughout southeast Wisconsin due to the flooding and lightning.