Results of a Randomized Hail Suppression Experiment in Northeast Colorado. Part IX: Overall Discussion and Summary in the Context of Physical Research

The three-year, randomized hail suppression test of the National Hail Research Experiment (NHRE) used seeding methods patterned after the Soviet hail suppression activities, applied over a specified target area on a randomly selected portion of days identified as having a high potential for hailfall by a radar criterion. Statistical tests for seeding effects were performed on data from ground networks of hail measuring instruments within the target area using total hail mass within the target area as the primary response variable. The statistical results indicate a range of possible mean seeding effects from a reduction of 60% to an increase of as much as 500% in total hail mass, depending on the test used, within the 90% confidence limits. The range is so wide that no conclusion about a seeding effect can be drawn. Analysis of hail size, embryo type and various radar parameters, and stratification either in terms of estimates of “hail potential” or operational seeding efficiency have also not re...