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Show seeding effects were found for cloud top temperatures :2: -20°C, with smaller" r negative effects for colder conditions. Higher silver concentration in collectect seeded snow samples (compared to unse e ded samples) was significant at the I 0. 1% level, as was the change of crystal habit to increased numbers of hexagonal plates during seeded periods. Thus, the stratification routines were quite effective in combination with statistical testing for obtaining definitive answers from such a small data sample. 11 The second analysis routine employed in 1968-69 was that of making detailed case studies where all types of collected data for any particular operational period were studied in concert. This scheme contributes to better understanding of the pattern of events over the area, since it forces attention to many details that might otherwise be lost. It frequently revealed good mutual agreement among the records of snow sample silver concentration, populations of snow crystal replicas with AgI centers, precipitation rates, and the computec arrival time of seeded precipitation. It is definitely a very valuable analysis routine. 6. 6 Feasibility of Engineering Application The main purpose of the project was to obtain a definitive answer as to whether or not it is physically and economically possible to augment precipitation in the headwaters of drainage basins by engineering-scale application of weather modification techniques to moisture-transporting air masseso Results obtained in the analysis of Park Range data allow a limited affirmative answer to this main question. The data show (from ex post facto data stratification) that, given perfect predictions of precipitating cloud top temperature, precipitation increases of > 100% would be possible for the Park Range when cloud top temperatures were -20 °C, by using a combination of ground and airborne seeding. Detrimental seeding effects (present when cloud top temperature -20°C) could be eliminated, resulting in net seasonal increases of as much as 100%. Perfect predictions of cloud top temperature behavior are not possible, however In fact, transient mesoscale vertical motion fields create rather large and frequent departures of cloud tops from any average altitude. With the aid of an additional radiosonde station 30 to 50 miles upwind, short period cloud top temp erature fluctuations should become sufficiently predictable to allow s.easonal cumulative seeding effects to amount to 25% to 40% increases in precipitation. Seeding without regard to precipitating cloud top temperature is indicated to yield little, if a~iy, overall net effect on a seasonal basis. This estimated possible magnitude of seasonal precipitation increase due to seeding over the Park Range was derived from Mt. Harris cloud top temperatur 334 |