Flash Flood and Flooding in Wisconsin, May 18, 2000

Leftover thunderstorms from the evening of May 17th eventually moved through Kenosha County during the pre-dawn hours on the 18th, and left in their wake flash flooding conditions around Somers. WSR-88D Doppler radar estimated that 2 to 3 inches fell in about 1.5 hours on top of saturated soils. Flood waters quickly reached 2 to 4 feet over roads resulting in gravel shoulder washouts. Eight families had to be evacuated by boat from their mobile homes as a nearby river quickly spilled out of its banks. Many vehicles were stranded in the high water levels, and many homes sustained significant flood damage to landscaping and interior home contents. In the western part of Kenosha County, at New Munster, the Fox River rose above flood stage at 1230CST on the 18th, crested at 12.31 feet on May 20th, and remained above the 10 foot flood stage into June, 2000. Up river at Pewaukee in Waukesha Co., the Fox River rose above flood stage on May 19th at 0000CST, crested at 11.71 feet on May 20th, and went below flood stage of 10 feet on May 22nd. Other mainstem rivers in southeast Wisconsin also went .5 to 1.5 feet above flood stage due to the heavy rains of May 17-18.The flash flooding over Kenosha County was a prelude to another series of severe thunderstorms that pounded south-central and southeast Wisconsin with damaging straight-line winds and large, damaging hail. Normally this part of Wisconsin doesn't experience so many thunderstorms that dump large hail. A supercell thunderstorm moved east/northeast across Iowa County. Hailstones up to 2.00 inches in diameter pelted and damaged many vehicles and home sidings, while stripping some of the corn and soybean crops. This storm then headed east into Dane County where it unleashed damaging straight-line winds in addition to large hail. Winds were estimated to reach hurricane-force level as the storm tore through Fitchburg where a home's garage was blown over. The storm then hit Madison with powerful winds and golfball size hail. A Madison home's roof was torn off by the winds, and many large trees were felled. At least 200 vehicles sustained moderate to severe hail damage in Dane County. Torrential rains dumped 1 to 2 inches of rain that resulted in urban flooding in Waunakee (Dane Co.). Milwaukee Mitchell Field set a new 24-hour rainfall record for May 18th with 1.53 inches, breaking the old record of .88 inches set back in 1968. Likewise, Madison Truax Field set a new record of 2.09 inches. After pounding Dane County the cluster of severe storms moved east all the way east to Lake Michigan by late morning, dumping large hail 1 to 2 inches in diameter in scattered locations. Once again, many vehicles were dented by the large hail. In fact, as in the Madison area, the ground was covered white by the hailstones in the Cedarburg/Grafton (Ozaukee Co.) and Kenosha (Kenosha Co.) area. The Black Earth Creek flooded after a 2-day rainfall of 6 to 8 inches over northwest Dane County. Soil erosion and minor damage to residential landscaping, including basement flooding, was noted along the stretch of this creek from Mazomanie to Black Earth to Cross Plains.Lightning strikes and tree branches brushing power lines left about 7000 customers over southeast Wisconsin without electrical power on the 18th. Additional scattered severe thunderstorms developed during the afternoon hours and dumped large hail stones as the Nebraska low which moved into eastern Iowa during the morning hours moved to northern Illinois by late afternoon. Southeast of the low air temperatures were in the 80s and surface dewpoints were in the 70s.