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days of interest to scientists (i.e., days with significant convective development) are also days for which severe weather watches or warnings affecting the project area are issued by the NWS. To avoid even the appear- ance that cloud seeding causes or aggravates severe weather, Water and Power suspends activities on days with forecasts of tornadoes, severe thunderstorms, hail, strong surface winds, or heavy precipitation. With this restriction, too few experimental days remained to justify continuing that field effort. Activity in the Montana High Plains during fiscal year 1979 was concentrated on the first in a series of experiments aimed at establishing the physical basis for enhancing beneficial growing-season precipitation from convection in the High Plains. Called HIPLEX-1,l! the experiment focuses on small, semi-isolated cumulus congestus clouds and explores the hypothesis that both the probability and amount of rainfall can be increased by means of ice embryo seeding for microphysical effects. The experiment relies on independent but coordinated physical evaluations to establish the cause and effect relation- ships for any modifications to the cloud and precipitation processes. During the fiscal year 1979 period, 12 clouds were treated by seeder aircraft in Montana and the effects observed by the University of Wyoming King Air cloud physics aircraft. In future seasons, a ground-based network of weather stations will measure and record precipitation, windspeed and direction, humidity, air pressure, and temperature. Results from cloud physics studies indicated that ice nuclei development within the clouds was enhanced by dry ice seeding. Response variables which measure precipitation later in the lifetimes of the clouds are not yet conclusive and will require further study in future field seasons. The 1979 activities in Texas emphasized the sampling and/or seeding of semi-isolated growing cumulus clouds. The clouds were seeded and observed by three aircraft. All seeding was performed with silver iodide flares. A network of 25 solar-powered automatic weather stations installed in and adjacent to the Texas HIPLEX study area measured and recorded temperature, relative humidity, pressure, windspeed and direction, and precipitation. In addition, 81 fencepost and 106 recording rain gages were placed on a grid throughout the study area to gather representative rain measurements. The States of Montana and Texas are sponsoring studies to learn the advantages and possible disadvantages of additional rainfall to the economy, the environ- ment, social considerations, and water supplies. Agricultural, municipal, industrial, and recreational uses are also considered. ~ Nearly 70 scientists, technicians, and pilots from universities, the private sector, and state agencies, plus 15 Water and Power scientists and technicians are engaged in HIPLEX field research, analyses, and assessment. ~ 1/ "The Design of HIPLEX-1, A Randomized Rain Augmentation Experiment on Summer Cumulus Congestus Clouds on the Montana High Plains," USDI, Bur. Reclam., April 1979. 6