"All of the sudden these storms busted through," ABC7 Meteorologist Mike Caplan said. "Large hail is going to be possible, and also tornadoes."
The severe weather led Metra to hold some outbound trains downtown due to high winds. Airlines also preemptively canceled 328 flights at O'Hare International Airport; No flights have been canceled at Midway.
Northwestern University canceled its evening events, including final exams, on both Evanston and Chicago campuses. The White Sox game at U.S. Cellular Field was also canceled, along as the opening night concert of the Grant Park Music Festival at Chicago's Millennium Park.
Several small tornadoes, quarter-sized hail and winds of up to 80 mph were reported. Emergency officials say tornadoes touched down in Winnebago County, but no major damage was reported.
The storms are part of a major system moving across the Midwest.
A Severe Thunderstorm Warning is in effect for Cook, DuPage, and Kane, Grundy, Kankakee, Kendall, LaSalle and Will counties in Illinois until 6:45 p.m.
In Indiana, a Severe Thunderstorm Warning is in effect until 7:30 p.m. for Jasper, Lake, Newton and Porter counties.
A Tornado Watch is in effect until 9 p.m. for several counties in Illinois, including Grundy; Kane; Kendall; Livingston; McHenry; Boone; De Kalb; La Salle; Lee; Ogle; and Winnebago. Several Wisconsin counties - Dane; Green; Iowa; Jefferson; Lafayette; Rock; Sauk; Walworth- are also under a Tornado Watch until 9 p.m.
A Severe Thunderstorm Watch is in effect until 1 a.m. for Cook, DuPage, Ford, Iroquois, Kankakee, Lake and Will counties in Illinois.
In Indiana, a Severe Thunderstorm Watch is in effect until 2 a.m. for Adams; Allen; Benton; Blackford; Carroll; Cass; De Kalb; Elkhart; Fulton; Grant; Howard; Huntington; Jasper; Jay; Kosciusko; La Porte; Lagrange; Lake; Marshall; Miami; Newton; Noble; Porter; Pulaski; St. Joseph; Starke; Steuben; Wabash; Wells; White; Whitley counties.
In Wisconsin, a Severe Thunderstorm Watch is in effect until 1 a.m. for Columbia; Dodge; Fond du Lac; Green Lake; Kenosha; Marquette; Milwaukee; Ozaukee; Racine; Sheboygan; Washington; Waukesha counties.