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OOil222 Mean seasonal snowfall increases over the direct detection phase target area are expected to be about 1 pct of the natural snDwfall_ Such small increases are more than two orders of magnitude smaller than the 400 pct natural variability of April 1 snowpack water equivalents observed during the periods of record on the two mountain regions. Detection of such small increases requires specialized instrumentation and approaches because they cannot be resolved by conventional precipitation gauging methods. 4.2 Scheduling During the Direct Detection Phase The direct detection experiments will be designed in final detail during the first year of the program, while environmental compliance activities are ongoing, and field support and analysis contracts are being let. However, many of the experimental specifics are stated in this and the remaining subsections of section 4. Field work will take place from about November 1 to March 31 each winter. Snowfall is likely in the mountains throughout this 5-mD period. This long field season increases the number of experiments that can be conducted each winter. To maximize the number of experiments, two crew shifts will be available to operate equipment on a 24 h d-1 basis when storms are present or anticipated. Operating day or night substantially increases the number of experiments possible per winter compared with only daytime operations, but at limited incremental cost because observing systems and facilities are in place no matter how often used. Sundays will be taken off because experience has shown a fixed day off each week greatly improves crew morale and effectiveness during lengthy field programs. Additional time off may be taken during periods forecast to have little chance of weather suitable for experimentation. ,. When conditions are suitable, radars, rawinsondes (weather balloons), microwave radiometers, ground vehicles, and all other equipment will be used day and night as needed. However, for reasons of safety, the research aircraft will be used only during daylight hDurs_ Nighttime aircraft sampling could be done, but would require a minimum sampling altitude at least 1,000 it higher than used during daytime. This additional altitude is needed to increase the safety margin in case heavy icing or mechanical problems necessitate a forced landing. As a consequence, nighttime sampling often would be above the seeding plume, so uSeful information would be limited. Nighttime in-cloud aircraft sampling is not recommended during the CREST. I' Even without the aircraft, reasonably complete direct detection experiments can be conducted during periods of darkness. As will be discussed, several direct and remote sensing systems will be operated to compare precipitation within and crosswind of the seeded zone. When available, the aircraft will document the location of the seeded zone's upper portion and associated microphysical effects. Although such information is needed for a large fraction of the direct detection experiments, it is not mandatory for all of them. 19