The National Weather Service in Indianapolis issued flood warnings for waterways including the White River and the Big Blue River.
Forecaster said there will be a 60 percent chance of rain from 5 to 7 p.m. on Saturday.
For Friday, it is expected to rain until about noon, with wind gusts up to 30 miles per hour and temperatures in the 50s.
Alex Manion, also a National Weather Service meteorologist, told The News that "The Metro Detroit area is in the bullseye for the heaviest amount of rainfall".
That warning, which encompasses Little Rock and Hot Springs, is in effect until 9:15 p.m. Wednesday.
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At 10:37 a.m., the State College-based weather service reported, minor flooding had already begun across the southern half of central Pennsylvania.
Sunday afternoon and evening could bring thunderstorms packing hail, gusty winds, lightning and locally heavy rain.
Gregorio said a slight chance of rain exists for Saturday, making Sunday the better of the two weekend days for any outdoor plans. However, there is still the potential that additional heavy downpours or thunderstorms could drag down some strong winds from higher up in the atmosphere.
Saturday - Cloudy skies with a few showers. It will contribute to the aforementioned big change in weather conditions, causing temperatures to be much cooler than what was experienced in April. Mostly cloudy, with a low around 49.