A tornado watch is in effect for several Illinois and Wisconsin counties.
Today started quietly in Chicago. It will not end that way.
After a foggy morning gave way to a dry and mild afternoon, forecasters say a line of potentially severe storms is set to push through the region between 5 p.m. and midnight, bringing with it the full range of threats: tornadoes, damaging winds, large hail, and flash flooding that could worsen conditions along rivers already running well above normal.
The Storm Prediction Center has placed most of the Chicago area under a Level 3 enhanced risk for severe weather, the third of five tiers on the scale. Northwest Indiana sits one level lower at Level 2. Meteorologists say all weather hazards are possible with this system, and residents in the affected counties should not treat this as a routine evening storm.
What the timeline looks like
Storms are expected to begin pushing into the far western suburbs between 5 and 7 p.m. The most intense activity should arrive in the city between 8 and 10 p.m. before tracking east into northwest Indiana. Rainfall rates of 1 to 2 inches per hour are possible during the heaviest bands, according to forecasters, which raises serious concerns for areas already dealing with saturated ground.
A tornado watch is in effect until 8 p.m. for DeKalb, LaSalle, and McHenry counties in Illinois, as well as Racine, Walworth, and Kenosha counties in Wisconsin. Separate flood warnings are active for Cook County until 5:15 a.m. Saturday and for Kane, Kendall, Lake, and McHenry counties until 5:30 a.m. Saturday. A broader flood watch covers the greater Chicago area until 5 a.m. Saturday.
Saturday morning could see some lingering showers, but skies are expected to clear through the afternoon. Temperatures will drop noticeably after the cold front passes, sliding from the low 70s Friday into the 50s for the weekend. A frost risk is possible Sunday night into Monday before temperatures climb back toward the 70s by Tuesday.
Rivers already swelling before the storms arrive
The concern for flooding is not hypothetical. Residents along the Des Plaines and Fox Rivers have spent much of the week watching water levels climb, and the prospect of another round of heavy rain has put entire neighborhoods on edge.
Officials have already reinforced areas along the Des Plaines River that are prone to flooding. Fire department crews are actively monitoring river levels, which are now expected to crest below the major flood stage threshold of 17 feet, a somewhat better outcome than earlier projections suggested. Still, authorities are urging residents to stay completely out of any standing floodwater, warning that hidden currents and displaced manhole covers create serious hazards that are difficult to spot from the surface.
The Fox River has also seen flooding this week, and residents nearby are taking similar precautions. In Chicago proper, the city has already fielded hundreds of calls about flooded basements and waterlogged streets, a sign of just how saturated the ground has become ahead of Today’s system. The public works department is making sandbags available to anyone who needs them.
An unusually active season
Meteorologists at the National Weather Service say Illinois is having a notably active severe weather season, and Today’s system is the latest in a series of events that have kept residents and emergency managers on their toes. A professor of meteorology at Northern Illinois University noted that the frequency of events this season creates an opportunity for residents to educate themselves about how to read and respond to official watches and warnings, rather than treating each new alert as background noise.
The advice from officials is consistent: monitor the National Weather Service and local forecasters, know the difference between a watch and a warning, and have a plan before the storms arrive.