How much did it rain in September? We would love to tell you. There was just 0.94 inches of precipitation to the Great Miami River Watershed. That is 2.22 inches below the monthly average. The station at Miamisburg recorded the highest amount during the month - 2.71 inches. and the station at Bellefontaine recorded the lowest amount - a mere 0.19 inches. As of September 30 we are 1.66 inches below average for this point in the calendar year in the Great Miami River Watershed.