Severe weather affected the northern two-thirds of central Illinois during the afternoon and evening hours of Thursday, June 10th. Numerous reports of funnel clouds and damaging winds were received as thunderstorms rapidly developed across the area. In addition, torrential rain fell across east-central Illinois, where flash flooding became a problem during the overnight hours.
Early in the day on June 10th, a nearly stationary frontal boundary stretched from southern Wisconsin into Iowa. To the south of the front, a southwesterly wind flow was transporting deep atmospheric moisture into central Illinois. As a result of an upper level disturbance, a large area of light to moderate rain had developed during the overnight hours across northern parts of the area. The morning rain was mainly confined to locations along and north of I-72...with areas to the south remaining dry. After sunrise, temperatures quickly climbed well into the 80s across southern Illinois, where skies were mostly clear. Meanwhile, the cloud cover and rain kept temperatures in the lower 70s further north across much of central Illinois. The rain area diminished and lifted northward by midday, leaving behind a rather pronounced temperature gradient that would later serve as the focusing mechanism for scattered severe storms later in the afternoon.
After a few hours of sunshine, scattered thunderstorms began to develop in the rapidly destabilizing environment. Storms that developed or moved close to the differential heating boundary left behind by the morning rain began to show signs of rotation on radar. Funnel clouds were reported as several mini supercells tracked northeastward across the area...with the strongest storms affecting Tazewell...Logan...and McLean counties. Eventually, the boundary across the region began to weaken and lift northward, diminishing the threat for rotating storms. After that, some of the storms began to take on a more linear structure, resulting in damaging winds in a few locations, including a 75 mph gust at the NWS in Lincoln.
As the evening went on, the threat shifted from severe weather to heavy rain and flooding. Numerous thunderstorms tracked across parts of east-central Illinois, dumping tremendous amounts of rain. The SWOP observer near Bismarck in Vermilion County picked up 5.10, while the Philo SWOP reported 4.44. As a result of the heavy rainfall, many fields and roadways became covered with water, prompting the issuance of flash flood warnings for these locations.