National Weather Service United States Department of Commerce
First Significant Severe Weather Event of the Season for Northeast Wisconsin


Event Overview

Severe storms produced large hail and damaging straight-lines across central and east-central Wisconsin during the evening of Tuesday June 2, 2020. Hail as large as 2 inches in diameter and wind gusts of 65 to 70 were reported generally south of Highway 10 between 6 pm and 9 pm Tuesday evening (Figure 1 - see Storm/Rainfall Reports tab). The storms were also accompanied by torrential rainfall with widespread 1-2 inches of rain reported (Figure 2 - see Storm/Rainfall Reports tab), producing mostly minor flooding. Hundreds of residents also lost power due to fallen power lines and lightning strikes. The severe storm outbreak was the most significant so far this convective season in northeast Wisconsin.

Environmental Overview

An upper-level disturbance and associated cold front approaching from the Dakotas interacted with a hot and humid airmass situated over Wisconsin late Tuesday afternoon. The key ingredients that ultimately led to the formation of severe thunderstorms were strong upper-level winds and extreme instability. A mid-level wind maximum (green colored area in Figure 6 - see Environmental Overview tab) associated with the upper-level disturbance, created favorable vertical wind shear to support long-lived storms. Meanwhile, sunny skies allowed temperatures to soar into the 90s, with several locations breaking record highs including Green Bay, Rhinelander and Wisconsin Rapids. The hot temperatures and high moisture content allowed extreme instability to develop during the day, especially over the southern half of Wisconsin. A measure of airmass instability is called Convective Available Potential Energy (CAPE). CAPE values reached 3000 to 4000 J/kg over southern Wisconsin which caused storm updrafts to be very intense.

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