In Fig. 4. This is a very good yield for dryland corn, but is not unreasonably high. However, we need to be cautious. Many years available water in the soil profile the last day of April may be less than 8 inches. Also, precipitation that falls during silking and pollination, influences corn yields more than that which falls at other growth stages.
Timing can be as important as total amount of precipitation received.
Pollen shed lasts about 9 days. So, for maximum pollination, we need at least 3 inches of water available to the crop during this period. Again, some of this water can fall as rain and some can come from soil water storage. A rainfall-probability distribution for this three week period would be helpful. But soil water available during this time is just as important.