The doppler radar rainfall estimates indicate that between 4 and 7 inches of rain fell over parts of Greene, Macoupin, and Montgomery counties in Illinois. This area received heavy rainfall from both the afternoon and evening rounds of storms. These estimates are confirmed by cooperative observe rainfall reports of 5.15 inches in Greenfield and 4.20 in Nokomis. The radar also indicated between 2.5 and 5 inches stretching from western St. Charles county, Missouri to Marion county, Illinois. However, this is a good example of overestimation of precipitation by the radar because of hail contamination.
Hailstones reflect more energy back to the radar than raindrops, causing the overestimation.