Weather service warns of conditions for isolated tornadoes
Gathering storm clouds from the west approach a freight truck parking lot and a strip of businesses at Lake Street and 25th Street in Melrose Park. (Chuck Berman, Chicago Tribune / August 23, 2011)
The storms are coming in two waves.
The first has already started to arrive in the western reaches of the Chicago-area, dropping significant rain in some places as it proceeds east at about 35 mph. ChicagoWeatherCenter.com says that the storm is weakening as it moves, but there were reports that it left an inch of rain in DeKalb County in less than 40 minutes.
That storm was weakening as it continues to slide to the southeast. Brief wind gusts up to 40 mph and heavy downpours are possible before the storms end early this afternoon.
Additional strong to severe tunderstorms ae expected to develop across northern Illinois late this evening through tonight.
Some of those thunderstorms could produce heavy rain, damaging winds in excess of 60 mph, quarter-size hail, frequent cloud-to-ground lightning and isolated tornadoes, the weather service warned.
The outlook covers Winnebago, Boone, McHenry, Lake, Ogle, Lee, DeKalb, Kane, DuPage, Cook, LaSalle, Kendall, Grundy, Will, Kankakee, Livingston, Iroquois and Ford counties in Illinois. It also covers Lake, Porter, Newton, Jasper and Benton counties in northwest Indiana.
Thunderstorms are likely again Wednesday, and there is a "slight risk" some of those may be severe, the weather service said, particularly over east central Illinois and northwest Indiana. The greatest threat will be damaging winds, large hailstones and locally heavy rainfall.
There is a slight chance of thunderstorms Saturday night into Sunday across portions of northern Illinois, and a chance of thunderstorms across the entire area Monday.