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1 1.0 INTRODUCTION ~ A major mechanism for producing wintertime precipitation in the . western United States is the forced lifting of air by the topography. The modification potential of these cold orographic clouds was first pointed out by Bergeron (1949) and further developed by Ludlam (1955), They hypothesized that the number of naturally occurring acti'Je ice nuclei may be insufficient to optimally convert supercooled cloud water to ice crystals and thus precipitation. If artificial ice nuclei could be introduced into a cloud in the above condition, then a more efficient precipitation yield would occur. Another effect of seeding can be a change in the buoyancy of a parcel due to changes in latent ~ heat release (Grant, et a1., 1969; Chappell, 1970). The latent heat effect is generally considered small for cold orographic clouds. ~ - Early modification programs made little attempt to scientifically ~ explain or examine the physical processes operating in the clouds. About a decade ago, Colorado State University (Grant, et al., 1971) began the first modification experiment with good statistical and scientific design. This and other programs (Rhea, et al., 1969) have steadily increased the understanding of the physics of cold orographic clouds. Presently, detailed models of operational modification programs are beginning. The change from modification experiments to operational programs ~ demands careful transition and design. Also, an eye should be kept on the future development of technology. This paper presents an ob- . servationa1 case study of an unmodified cold orographic cloud. Our