The National Weather Service has issued a tornado watch for all of northern Illinois until 8 p.m. Saturday.
The Storm Prediction Center has placed most of the region under an enhanced risk for severe storms with all severe weather hazards possible, including a few tornadoes, large hail and isolated damaging winds gusts.
Storms were already forming over western Illinois as of 12:30 p.m. The threat for severe storms will spread east and continue through the evening.
In addition to severe weather, any storm that develops will likely produce locally heavy rainfall, which could lead to isolated flash flooding and renewed rises in area rivers.