WMOD00413

• Title: Validation of Precipitation Management by Seeding Winter Orographic Clouds in the Colorado River Basin
• Date: 9/1/1993
• Weather Modification - Doc Type: Report

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A local advisory committee will be formed to monitor and advise the program, and to serve as
the focal point for public awareness. A series of public meetings will be held prior to the seeding
experiments to assimilate any public concerns into the project design. Local concerns and
advice will be incorporated into development of suspension criteria and the environmental
monitoring plan.

Statistical analyses of some earlier experiments and operational projects suggest seeding of all
suitable storms might produce seasonal snowfall increases of 10 to 15 pct. Thus, seeding during
the statistical experiment might increase the seasonal snowpack by perhaps 5 to 8 pet, because
only half the experimental units will be seeded based on random decision. But seeding during
direct detection experiments will be constrained to brief (2 to 4 h) periods, and will take place
only once or twice per storm day. Furthermore, seeding agents will be released from only one or
two sites during any experiment, so the area affected will be limited. The crosswind distance of
the seeded zone will deliberately be minimized to reduce the effect of natural spatial variations
on snowfall assessment. Crosswind control gauges located near the target provide a better
prediction of the nonseeded portion of the target snowfall.

Mean seasonal snowfall increases over the direct detection phase target area are expected to be
about 1 pct of the natural snowfall. 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-mo 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 dol 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 hours. Nighttime
aircraft sampling could be done, but would require a minimum sampling altitude at least

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