In those regions, meteorologists say, the main concerns will be damaging winds and the possibility of a few tornadoes.
The Watch takes effect Tuesday evening and remains in place through late Wednesday night.
According to the National Weather Service, the combination of heavy rain and melting snow will cause flooding along some rivers in northern IL and northwest Indiana.
Flood stage is 9 feet, according to the weather service.
Flood stage of the Fox River in Burlington is 11 feet, which is about the level at which the river was forecast to crest by the National Weather Service's Sullivan office.
The rain forced road fix crews to put emergency work scheduled for Monday on hold. Potholes in this area have been repaired.
The persistent freeze-thaw pattern over the winter has left roads crumbling and in particularly poor condition, she said.
Hoppenstedt said the frozen ground has created more runoff than usual.
Meanwhile, temperatures will be mild. Record breaking 60s are expected this afternoon.
The record for highest daily temperature for February 20 is 63, set in 2016.
See images of Metro Detroit flooding this week. And that means spring-like flooding is possible. The total rainfall through noon Wednesday could be over two inches.
A 40 percent chance of showers Wednesday is forecast to by joined by a high temperature of near 65 degrees.
Today's high, if it reaches 69 degrees as predicted, would set a new record for the date.
"There will be a lull Thursday before it [the rain] ramps back up Friday and Saturday, and then dry out on Sunday", he said.
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