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A balance among northern. central. and southern High Plains research was considered necessary to bring out similarities and differences among rain pro- ducing systems in this region. Previous studies had shown distinct climatic variations in convective clouds and precipitation from north to south over the Plains. Convective clouds over the southern High Plains tended to have more moisture. warmer and lower cloud bases. and were found to be generally more vigorous than those over the northern High Plains. In the southern plains. where cloud bases are warm. and liquid water concentrations are relatively high. raindrops often form by coalescence of liquid qloud droplets. although the ice process is still responsible for most of the natural precipitation from these clouds. In the northern High Plains. where cloud-base temperatures are near 0 0 C (32 0 F) and liquid water concentrations are low. precipitation generally is initiated through an ice process. It was decided that three field sites should be estab- lished to investigate variations with latitude as well as to identify the common factors in High Plains con- vective clouds. In keeping with the concept devel- oped in the ISWS plan. a systematic progression at each site was planned;operations at each site would progress from observations to experimental seeding of individual clouds to area-wide experiments. This approach was considered to be fundamental to both the ISWS plan and the directive which had estab- lished HIPLEX. Points considered in selection of field sites included the presence or absence of commercial seeding projects which might confuse the results of scientific experiments. the willingness of State Governments to cooperate in data collection and analysis. the atti- tudes of local residents. and logistics. Logistical con- siderations included the location of airports needed for research aircraft. roads for servicing precipi- tation gages. and so on. After considerable study. field office sites were selected at Big Spring. Texas; Goodland. Kansas; and Miles City. Montana. Figure 2.4 shows these loca- tions as they appear on a satellite photograph. 2.5 Field Experiments and Technology Development The status of each site for each season is shown in figure 2.2. Following some preliminary observations with a 3-cm radar at Miles City in 1974. systematic data collection began at all three sites in 1975. Each site was equipped with at least one weather radar set and standard meteorological instruments. As time went on. some degree of specialization emerged. For example. fexas HIPLEX emphasized Figure 2.4-Satellite imagery helps track storm development. the collection of data from a network of rawinsonde stations installed as part of the project. Some of the equipment obtained for HIPLEX was used on a rotating basis among the three sites. This arrangement was most often used for expensive equipment such as jet aircraft carrying special instrumentation for high-altitude cloud physics observations. By 1976. HIPLEX was in full swing with data being collected at all three sites and stored at the Denver Federal Center. The original intent of the ISWS Plan was to proceed with each phase of observation. experimentation. and area seeding at each of the three sites concurrently. As the project progressed. HIPLEX managers constantly evaluated results. By 1978. it was becoming increasingly apparent that the available funding for HIPLEX would not support full-scale programs at all three sites. Work in Montana had identified a class of clouds. isolated cumulus congestus. qn which seeding experiments could be conducted to answer some basic questions about seeding. Exploratory seeding in Texas had not progressed as far but was still regarded as encouraging. However. Kansas cloud systems appeared to be very complex. being similar to Montana clouds on some days. and similar to Texas clouds on other days. Moreover. early studies 8