Exploratory analysis of seeding effects on rainfall: Illinois 1989

Radar-indicated rainfall characteristics from six experimental units randomly selected for AgI treatment were compared with those from six experimental units treated with sand during the summer of 1989 in an exploratory analysis. No differences were found between AgI and sand cell frequencies before and after treatment. The areal extent of rain in all AgI-treated units grew during treatment, whereas four of the sand units decreased, but the differences were not significant. This study found some weak evidence of augmented rainfall due to seeding but the sample size is too small to draw definitive conclusions of an effect. As in many other seeding experiments, results suggest that if a seeding effect occurred, it was present during only certain atmospheric conditions (some frontal situations producing heavy rain) and only with certain clouds (rapidly growing congestus treated in the early stages of development). -from Authors