Flash Flood in Dane County, Wisconsin

A 1-in-a-100-year flash flood occurred from the west side of Madison to around the Capitol Square after 3 to 5 inches of rain fell within a 90 minute timeframe. There were no reports of injuries or deaths. The heavy rain resulted from slow-moving and back-building thunderstorms that essentially remained nearly stationary over the city of Madison. The hilly terrain and a typical urban setting of a lot of concrete and asphalt enable the runoff water to quickly overwhelm the storm sewers and concentrate water in low-lying areas of the city. Water depths reach to the top of small vehicles - 4 to 5 feet deep in spots. Many roads became impassable due to the flood waters, and many residential homes and businesses on or near the UW-Madison campus had flooded basement and first-floor flooding. Some basement apartment units had water depths of 6 to 8 feet. Nearly all campus buildings had flooding of varying degrees of intensity, and the Camp Randall football field sustained damage. Some campus buildings had flat roofs that quickly flooded as storm drains became plugged - which allowed water to run thru the walls and ceilings of buildings. The buildings that sustained the most damage were the Memorial Union, Computer Sciences, and Veterinary Medicine. Numerous vehicles on or near the campus were damaged or totaled by the flood waters, and some were reported to be floating away. Unofficial rain gages measured 4.5 to 5 inches from just west of West High School up to the Capitol Square. WSR-88D Doppler rainfall estimates were in the 3 to 5 inch rain, therefore it appears the unofficial rain gages were very accurate. Rainfall amounts quickly fell off to 1 to 1.5 inches near the south Beltline (STH14/18/151). It is nearly impossible to assess the monetary value of the flash flood damage, therefore, the amount posted in the header strip of this event is only a ballpark 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.