Flash Flood in Waukesha County, Wisconsin

A 1-in-a-100-year flood occurred in and around the city of Waukesha after a heavy rain of 3 to 5 inches within a 2-hr period. The heavy rains were the result of slow-moving or back-building thunderstorms that essentially sat over the same area. There were no reports of injuries or deaths. Numerous roads and yards were flooded with water depths of 1 to 5 feet. Many vehicles were stalled in the deep waters or were damaged. There were numerous reports of flooded basements of homes or businesses or apartments. The roof of one business in downtown Waukesha collapsed due to the weight of the heavy rains. The Fox River in downtown Waukesha exceeded its 6-foot flood stage by 6 inches, and then quickly subsided. Some nearby farm fields reported washed out sections and crop losses. The Expo Center sustained damage as well to several of its buildings. The basement of the downtown Waukesha Fire Department flooded to the depth of 5 feet. This flooding was the result of a collapsed trench outside the building where a new addition was under construction. At one point, Waukesha city officials warned motorists to stay away from the city, and some officials thought the July 27th flooding was the worst they could remember. WSR-88D Doppler radar rainfall estimates indicated that up to 5 inches fell over the northwest portion of the city of Waukesha, tapering off to 2 inches on the far south side of the city where STH 59 is located. One unofficial rain gage catch was 4.25 inches on the north side of the city, which matched the radar estimate. It is nearly impossible to assess the monetary amount of the flash flood damage, therefore, the amount posted in the header strip of this event is only a rough estimate.

A similar scenario to that of July 9, 2006 occurred again on the afternoon of July 27th. Very slow moving scattered thunderstorms developed across portions of south-central and southeast Wisconsin. A lake breeze fired additional storms across Waukesha County. With propagation speeds often less than 15 mph, torrential rains resulted underneath these storms. Nearly stationary storms over the Madison and Waukesha areas produced 4 to 5 inches of rain within about 90 minutes. Flash flooding resulted in these locales with many buildings and vehicles sustaining varying degrees of damage. The UW-Madison campus was especially hit hard. See the specific write-ups as flash flood entries above. Other smaller cities in Dane and Waukesha counties also experienced some minor urban flooding, but these reports did not warrant a separate line-item entry above. Other storms across the area pulsed to severe limits to produce damaging winds to about 61 knots (70 mph) and one funnel cloud report at 1228CST at a location 2 miles northwest of Stoughton (Dane Co.). The major electrical companies estimated that about 10,000 customers were without electrical power at one time or another on July 27th, due to tree debris or lightning striking power-lines.