The National Weather Service has issued severe thunderstorm watch for the greater Chicago area until 11 p.m. Tuesday.
The watch includes 14 counties in Illinois. Eight counties are in northeast Illinois: Cook, DuPage, Grundy, Kane, Kendall, Lake, McHenry and Will. Six counties are in north central Illinois: Boone, DeKalb, LaSalle, Lee, Ogle and Winnebago.
The watch also includes Lake and Porter Counties in Indiana.
The approach of a cold front from the northwest along with a strong jet stream flow aloft will be enough to trigger severe super-cell thunderstorm development over eastern Iowa and northwestern Illinois during the peak-heating hours with storms moving east and south over the Chicago area later Tuesday afternoon into the evening.
Large hail will be the primary threat along with strong damaging winds in the stronger storms.