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r <br /> I <br /> Created 12/26/06 6 <br /> the target area and to determine whether it arrived there as a result of ice nucleation by the <br /> seeding material (32, 33, 34 and 35). One operational program in the Sierra Nevada used this <br /> trace chemical technique to show that cloud seeding operations produced a seasonal 8% increase <br /> in the snowpack over a specific watershed (36). Such results from physical and trace chemical <br /> analyses compare well with earlier randomized experiments such as that of PG&E (30) which <br /> showed similar increases in the northern Sierra Nevada. <br /> Conclusions and Recommendations <br /> The studies and experiments summarized in this paper represent millions of dollars <br /> worth of research effort conducted over many decades by meteorologists, physical scientists, and <br /> statisticians. We are currently operating under a well defined cloud seeding conceptual model. <br /> We have documented the potential impact of cloud seeding, the cloud conditions needed and the <br /> chain-of-events in effective cloud seeding. We have continued to develop new and innovative <br /> techniques for operations and for evaluations needed to prove cloud seeding effectiveness and to <br /> refine cloud seeding programs. The NAIWMC concurs with the World Meteorological <br /> Organization's policy statement that contends "well designed and properly conducted cloud <br /> seeding programs will produce demonstrable results". The NAIWMC also acknowledges recent <br /> advances in atmospheric modeling, remote sensing, and laboratory techniques and believes these <br /> new technologies can assist with advances in cloud seeding operations. We certainly concur <br /> with the main recommendation of the NAS report that a "coordinated national research <br /> program" is needed to apply the new technologies to key uncertainties in weather modification. <br /> Recommendations for evaluations of current operational seeding programs and for <br /> future research in snowfall augmentation include, but need not be limited to, the following: <br /> • Evaluate new or existing operational seeding projects (which have not done so) to <br /> document the initial steps of the conceptual model to ensure seeding in the SLW zone <br /> is actually occurring. The following techniques can be used. <br /> o Trace chemical analysis of snowfall in the target area. <br /> o Transport and dispersion studies using modeling,plume tracking, etc. <br /> o Air flow, temperature and SLW measurements over the project area. <br /> • Continued testing of silver iodide and liquid propane seeding methods. <br /> o Conduct relatively small-scale randomized experiments, which have been <br /> done on only a very limited basis in the past 20 years. <br /> o Use accepted statistical techniques with the randomized studies to analyze the <br /> magnitude of seeding effects. Use predictor variables to strengthen the <br /> statistical analyses and reduce the number of experiments needed to obtain <br /> significant results. <br /> o Support any statistical study with observations sufficient to enable <br /> understanding of the physical processes. <br /> • Test current, or develop new satellite and ground-based remote sensing techniques to <br /> detect cloud seeding potential and monitor seeding induced changes in clouds. <br /> The current NAIWMC membership includes state agencies in <br /> North Dakota,Kansas,Oklahoma,Texas,Colorado,Wyoming,Utah,Nevada and California <br />