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The following activities will occur from early November to late March to obtain data for the climatological program: 1. Precipitation gauges will be operated at several sites within reasonable oversnow access from Highway 65. Figure 4 shows typi- cal precipitation gauges. 2. Liquid water content of the clouds and air will be monitored at the Grand Mesa Observatory, using a Rosemount icing probe and heated anemometer atop the existing tower and a microwave radiometer (see figs. 5 and 6). ~ . 3. Wind speed and direction, air temperature, dewpoint tem- perature, and atmospheric pressure will be measured at the Grand Mesa Observatory. 4. Cloud presence will be estimated at the observatory from the temperature-dewpoint spread and by time-lapse photographs. Since this ongoing data collection activity is research non- manipulative of the environment as described in Bureau of Reclamation criteria for categorical exclusion under NEPA, these climatological studies are not included further in this environmental assessment. B. New Studies - Proposed Action Studies proposed to be initiated this year are: (1) transport and dispersion studies, to monitor the direction and horizontal and ver- tical dispersion of air- and ground-released AgI to understand the characteristics of dispersal of the plume of particles; and. (2) experiments to detect the physical changes in clouds that particular methods of seeding cause. . The work would be conducted principally during the Decernber-January-February period. For the programs described below, an aircraft would average about 40 hours per month flying over the mesa. During non-storm con- ditions, the aircraft can fly closer to the ground than with in-cloud conditions, and much of the plume tracing would be done under non- storm conditions in order to obtain data closer to the surface. Increased snowfall, when the experiments would include seeding clouds. usually would last less than one hour. The principles involved in seeding winter orographic clouds1 are briefly as follows. The flow of moist air over mountain barriers produces liquid water droplets through condensation as the air is forced into colder temperatures at higher elevations. These droplets ~ e Jorographic - of or pertaining to mountains. Orographic cloud - a cloud whose form and extend are determined by the disturbing effects of mountains upon the passing flow of air. 6