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<br /> <br />Ice particle sizes and trajectories in several cases are examined. <br />Indications are that the growth regions resul t ing from art ificial nucle- <br />ation are likely to be at altitudes close to the barrier-top level and <br />associated moderate or heavy riming results in relatively steep precipi- <br />tation trajectories compared to unrimed ice crystals. <br /> <br />It is emphasized throughout the report the need for randomiza- <br />tion in a study wherein seeding effects are sought. Only with randomi- <br />zation can the unseeded units be properly defined. <br /> <br />For the evaluation of historical data, precipitation in the target <br />area and in two control areas are used. Also, pressure and upper level <br />data are used to develop covariates. Increased precipitation in seeded <br />seasons relative to the historical record is found in some of the anal- <br />yses, part icularly in 1978-79-80 sea,!2!ls. The overall 8 season in- <br />creased precipitation ranges from 2% to 27%. depending upon the control <br />used. <br /> <br />Detailed analysis of data during the seasons of 1978-79-80 reveal a <br />more or less random. distribut ion of increased precipitation between <br />unseeded and seeded days. Also, use of a control area in California <br />shows that the apparent increase may be explained by other (unknown) <br />factors independent of seeding. It is concluded that either a more <br />extensive historical record orior to the seeding project is required ~ <br />covariates that remain stab Ie over the ent ire period of interest are <br />needed in order to make a meaningful evaluation of historir-..l d.ata./ <br /> <br />ii <br /> <br />--- ~ <br />