But just how much will Chicago get?
"We have various computer models we use, and they're all over the place," ABC7 Meteorologist Jerry Taft said Friday. "One thing they do agree on is the fact that most of the rain that we see over the weekend will be south of Chicago."
Rain is already following in parts of the Midwest. And it's expected to hit the Chicago area on Saturday evening or overnight.
"The heaviest rain will be south of the city and the lightest rain will be up to the north along the Illinois-Wisconsin border," Taft said.
Some forecasts predict as much as 7 inches on drought-parched parts of central Illinois. Chris Wise has spent weeks watching the corn in his fields wither in heat and drought. Friday, he hurried to save it from what could be weekend-long downpour across much of Illinois.
As gray clouds moved over his farm south of Champaign, Wise drove a combine into a corn field, hoping to harvest what he could before rain left the ground too muddy for equipment.
"We don't want another disaster," Wise said later Friday, as he prepared to drive a truckload of corn to an elevator.
State and local emergency officials prepared for the possibility of flash floods, while schools and other organizations cancelled or rescheduled events - from high school football games in Belleville and St. Joseph to the annual Labor Day parade in Urbana.
The Illinois Emergency Management Agency was ready with crews of prison inmates to fill sandbags and could call on resources, such as rescue boats scattered around the state, if need be, spokeswoman Patty Thompson said.
But the agency wasn't sure what to expect. Usually, a big rain this time of year would fall on creeks, rivers and lakes full of water. This year, that isn't the case.
"Things are so different right now with the drought going on," Thompson said.
Illini football, though, was almost certain to go on as scheduled, university sports information director Kent Brown said. The school has evacuation plans for lightning and severe winds, but otherwise the new artificial turf at Memorial Stadium should be able to handle the water, he said.
"The turf there can take something like (12) inches" in 24 hours, Brown said.
While heavy rain might keep some campers home, the agency that oversees state parks was hoping for a good soaking. That could allow the state Department of Natural Resources to lift burn bans that have kept campers from building fires in some parks for weeks, spokesman Chris McCloud said. And lakes used for duck hunting should start filling back up.
"There's nothing in particular that we prepare for, except for maybe get on our knees and thank the Lord that there's going to be some rain," McCloud said. "We haven't seen it in quite a long time."
The Associated Press contributed to this report. All rights reserved.