The National Weather Service of Pittsburgh has issued a flash flood warning for northwestern Butler County and parts of two other counties until 7 p.m. on Thursday, June 19.

Areas under the warning include Slippery Rock and Harrisville, and Cranberry Township is also listed as at-risk for flooding.

The service said as of 4 p.m., up to half an inch of rain has already fallen in the area. Southeastern Mercer County and southern Venango County are also under flash flood warning, according to the National Weather Service.

Additional rainfall amounts up to 1 inch are possible in the warned area, according to the service.