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<br />003485 <br /> <br />Correlations for courses within most basins reveal a relationship <br />of moderate strength. A strong relationship was not expected considering <br />the many assumptions made and the probable errors associated with using a <br />single upwind sounding to represent conditions over the entire state. <br />These coefficients indicate that it is possible to obtain fair estimates <br />of actual snowfall from interpolated rawinsonde .data. <br /> <br />Identifying Seedable Events <br /> <br />Atmospheric scientists agree that not all winter clouds or storms <br />are seedable, but they do not agree on how to identify the ones that are <br />seedable. Identification is difficult because the microphysics of cloud <br />formation and growth is complex and because the important roles of <br />convection, orography and large-scale meteorological processes in the <br />developnent of storms are not understood adequately. As these topics are <br />beyond the scope of this study, we chose to identify seedable events by <br />using the results of statistical analyses of previous field experiments. <br />We chose the definitions presented and tested by Mielke et al. (1981) in <br />their re-analysis of the Climax experiments. <br /> <br />Mielke et al. found that precipitation during Climax I and II was <br />25 percent greater on seeded days than on control days when the <br />temperature at 500 rob was equal to or warmer than -20 degrees Centigrade. <br />The probability that this increase resulted trom chance alone was less <br />than .002. When storms with 500 rob temperatures colder than -20 degrees <br />Centigrade were seeded, increases in precipitation were not observed. <br />Mielke et a1. also observed maximum increases in precipitation when the <br />wind speed at 700 rob was between 12 and 14 meters/second. Increases were <br />not noted for lower or higher wind speeds. Based on these results, we <br />considered a storm seedable if its 500 mb temperature was warmer than or <br />equal to -20 degrees Centigrade and its 700 rob wind speed was between 9 <br />and 16 meters/second. The Mielke wind speed criteria were broadened <br />because not all basins in the state have similar topography (Grant, <br />personal communication). We assumed that these modified criteria are <br />valid statewide. The validity of this assumption is not known. <br /> <br />26 <br />