The National Weather Service has issued a flash flood watch until Tuesday morning for an area that includes Mercer County, Ohio.
Showers and some embedded thunderstorms will develop across the area tonight, the weather service said in its announcement.
The showers are capable of producing heavy rain over the same location for a prolonged period, making flash flooding possible, the announcement said.
It said parts of the watch area already have saturated ground from previous rainfall, which makes the threat greater.
The weather service said flooding of small streams, creeks and other drainage areas is possible, and residents should be prepared for immediate action if heavy rains or flooding occurs, or if a flash flood warning is issued.