Flash Flood in Washington County, Wisconsin

Heavy rains resulted in flash flooding over much of Washington County. Water depths on road surfaces reached 3 feet or more and there were gravel washouts. Some farm fields would remain flooded into early July. The breakdown in residential home losses were: 560 affectd with minimal damage, 60 with minor damage, and 12 with major damage (total of about $2.4 million). Business losses were: 45 with minor damage, and 5 with major damage (total of about $1.125 million). Crops losses were estimated at 3.5 million. Public sector damage was about $0.6 million. Several roads and bridges sustained damage.

A slow-moving surface boundary, nearly parallel with the mid-level flow affected southern Wisconsin during the period of June 7th through June 9th. A strengthening low-level jet and strong moisture advection produced several rounds of thunderstorms during the period in the vicinity of this boundary. The atmosphere was very moist with precipitable water values around 2 inches. Low to mid-level wind flow supported training of flood-producing thunderstorms. A weak cool front pushed through southern Wisconsin late on the 8th/early on the 9th, finally ending the heavy rainfall.

The heavy rain axis for June 7-9th ran from Sauk County southeast to Milwaukee County, where generally 6 to 9 inches fell on a ground that was totally saturated due to record-setting winter snowfalls and a wet April, 2008. Several locations topped 10 inches, and Watertown (Jefferson Co.) came in with 13.5 inches, 11.35 inches was measured in Oak Creek (Milwaukee Co.), and Elm Grove in Waukesha County picked up 10.8 inches.