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<br />00022? <br /> <br />Both the Grand Mesa and the Wasatch Plateau are reasonably typical of high terrain in the <br />Basin. Both barriers have broad along-the-wind dimensions. Consequently. with typical winds. <br />ice crystals formed by seeding over the windward slopes should have sufficient time <distance) <br />to grow and settle to the surface before reaching the lee subsidence zone where cloud droplet <br />evaporation and ice crystal sublimation take place. Both barriers have moderate on top relief. <br />permitting low-level aircraft sampling during storms. Both areas have all-weather highways for <br />access to high elevations. and are amenable to DversnDw travel. Operational and experimental <br />seeding programs have been conducted on each barrier in the recent past. However. the <br />proposed experimental programs are much more comprehensive than the limited past <br />experiments. Both mountain areas have a high frequency of snowfall and SLW occurrence as <br />discussed in detail in appendix B. <br /> <br />4. DIRECT DETECTION EXPERIMENTAL PHASE <br /> <br />Section 4 discusses the CREST direct detection phase. including expected seeding impacts and <br />suspension criteria. experimental scheduling, the role of numerical modeling, and how seeding <br />will be conducted. The observations to be made during direct detection experiments, along with <br />their purposes. are discussed in detail. Procedures for a typical experiment are described_ <br /> <br />4.1 Seeding Impacts and Suspension Criteria <br /> <br />Environmental compliance activities will be finalized for each experimental area prior to any <br />seeding. The procedures involved in compliance are briefly discussed in section 8. and described <br />in detail in appendix D. An environmental monitoring plan will be developed and implemented <br />prior to seeding. <br /> <br />Suspension criteria will be developed prior to seeding. Seeding will be suspended during periods <br />of well-above normal snDwpack, serious avalanche danger, and possibly other periods when <br />addi tiDnal snowfall may be undesirable. Although the direct detection seeding experiments are <br />not expected to enhance the snDwpack to any significant degree, it would be prudent to avoid <br />the perception that seeding may have contributed to problem situations. <br /> <br />, <br /> <br />A local advisory committee will be formed to monitor and advise the program. and to serve as <br />the focal point for public awareness. A series of public meetings will be held prior to the seeding <br />experiments to assimilate any public concerns into the project design. Local concerns and advice <br />will be incorporated into development of suspension criteria and the environmental monitoring <br />plan. <br /> <br />Statistical analyses of some earlier experiments and operational projects suggest seeding of all <br />suitable storms might produce seasonal snowfall increases of 10 to 15 pct. Thus. seeding during <br />the statistical experiment might increase the seasonal snowpack by perhaps 5 to 8 pct, because <br />only half the experimental units will be seeded based on random decision. But seeding during <br />direct detection experiments will be constrained to brief (2 to 4 hl periods, and will take place <br />only once or twice per storm day. Furthermore, seeding agents will be released from only one or <br />two sites during any experiment, so the area affected will be limited. The crosswind distance of <br />the seeded zone will deliberately be minimized to reduce the effect of natural spatial variations <br />on snowfall assessment. Crosswind control gauges located near the target provide a better <br />prediction of the nDnseeded portion of the target snDwfall_ <br /> <br />18 <br />