July 17, 2006: Straight-line wind in Columbia, Dodge and Walworth Counties

Two rounds of severe storms affected parts of south-central and southeast Wisconsin on July 17th. The first round occurred during the early afternoon hours over the counties of Dodge, Fond du Lac, Washington, and Sheboygan. By 1250CST the storms had organized into a bow echo line extending from Lake Winnebago south to near West Bend and Hartford in Washington County and then west to the Columbus area in southeastern Columbia County. This bow echo then moved east to out over Lake Michigan. Dime-size hail and thunderstorm wind gusts up to 65 knots (75 mph) resulted with some of these storms. Tree and power-line damage was reported in addition to some structural damage in Dodge and Sheboygan counties. A semi-truck was also blown off InterState 43. After a brief lull from thunderstorms, more storms developed during the evening hours across the remainder of south-central and southeast Wisconsin. These storms produced dime to quarter-sized hail and wind gusts to around 52 knots (60 mph). Mainly tree damage was reported with these storms.Interestingly, the cluster of severe storms that affected the southern parts of Lafayette and Green Counties moved east-southeast to McHenry County in northeastern Illinois. A strong thunderstorm gust front (outflow boundary), associated with the McHenry County thunderstorms, pushed north into southeastern Wisconsin. The gust front winds knocked down some trees in the Twin Lakes-Trevor area of western Kenosha County, and the Eagle Lake area northwest of Kansasville in south-central Racine County. No precipitation was associated with these outflow winds in Kenosha and Racine County. Eventually this gust front merged with another south-moving frontal boundary over the central portions of Racine County. Severe thunderstorms quickly popped up in this merger zone over central Racine County, and eventually they moved southeast through the remainder of Racine and Kenosha Counties (round #2 of severe weather for July 17th). Synoptically, a strong, mid-level short wave trough traveled east through Wisconsin during the afternoon and evening hours. Hot temperatures in the mid-90s with dew points in the low to mid-70s, and cooler air aloft, caused extreme instability to increase through the day which allowed for rapid thunderstorm development.