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~ N ~ (.,.:-: ~ S's\--. \VI 't-~ EVALUATION OF CLOUD SEEDING IN UTAH INTRODUCTION Utah has had a cloud seeding program for six years with a snowpack augmentation project operating during each of these years. A rain increase! hail suppression project has operated during the past four summers. Many attempts have been made to evaluate the progress of the winter snowpack project, however because of a lack of data these evaluations were never statistically significant. The results of an operational project are much more difficult to determine than those of a research project. Operationally the sponsor's objective is to increase the precipitation, the maximum amount possible, thus all seedable storms are treated. On the other hand, the research objective * is knowledge; therefore, techniques such as randomization can be used to determine the effects. Earlier attempts at evaluation by the Division of Water Resources and North American Weather Consultants (NAWC) were unsuccessful in showing statistical significance because of a lack of data and also because the control areas which had been chosen were too far from the target areas. This past winter NAWC looked into the possibility of utilizing a control area in Western Utah much. closer to the target area. A discussion of the selection of the control area follows under a separate section. After selection of a more representative control area, trial data runs indicated that good relationships existed. NAWC then completed an evaluation study and after review by the Division of Water Resources' Technical Advisory Committee, the report was published. The following sections labeled Approach, Selection of Control, and Definition of Target Area are quoted directly from the NAWC report: *Randomization is a procedure where some seedable storms are left unseeded for comparison purposes.