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<br />Cloud liquid water was observed over 400 hours during the two field programs or, on average, about <br />100 hours per month. The vertically integrated mean amounts were less than 0.1 mm for over half the hours, <br />suggesting limited cloud liquid water contents as verified by aircraft observations. Similar liquid water <br />contents have been found during winter at a number of other mountain locations in the West; yet the times <br />with limited liquid may be important in future operational cloud seeding because the many hours of <br />occurrence could result in significant snowfall accumulation. Conversely, the infrequent hours with abundant <br />cloud liquid water may also have significant weather modification potential through potentially higher <br />snowfall rates. It is of interest that much of the seasonal snowpack in the western mountains is typically <br />produced by many hours with light snowfall. But the presence or absence of a few big storms with high <br />precipitation rates can result in large departures from a "normal" seasonal snowpack. <br /> <br />Cloud liquid water episodes varied in length from 1 to 80 hours, but the seven episodes lasting 30 hours or <br />more accounted for half the observed hours with liquid cloud over the radiometer. The overhead flow or <br />"flux" of cloud liquid water was estimated for each storm episode by incorporating windspeed measurements <br />at cloud levels. It was found that only three storms produced about 75 percent of the seasonal flux in 1987, <br />and a single storm provided approximately 67 percent of the 1988 flux. Both these fmdings further <br />emphasize the importance of the major storm events in seasonal cloud liquid water production and, thereby, <br />seeding potential. Ranges of observed cloud liquid water values were converted to probable precipitation <br />rates for ease of comprehension. It was shown that cloud seeding could rarely produce more than a few <br />millimeters per hour of snow water equivalent (or few centimeters per hour of snow depth) because, like <br />natural snowfall, seeding-produced snowfall is limited by the availability of cloud liquid water flux. <br /> <br />The total cloud liquid water flux for the two field seasons was compared with mean annual runoff from high- <br />elevation watersheds in the same areas. The 1987 flux was equivalent to about half the runoff while the 1988 <br />season, which had few large storms, had a flux equivalent to 14 percent of the runoff. For a first <br />approximation in the absence of additional data, let it be assumed that these values represent typical "wet" <br />and "dry" winters; then 4-month winter seasons would usually have cloud liquid water fluxes ranging from <br />about 30 to 100 percent of the mean annual runoff from the same high elevation watersheds. This is a <br />considerable amount of excess water passing over the barrier crests and gives cause for optimism about the <br />potential of cloud seeding. It is, of course, important to determine what fraction of the excess water can be <br />converted to additional precipitation by seeding. But even conversion of a small fraction into additional <br />precipitation could be quite beneficial in enhancing streamflow and ground-water supplies. <br /> <br />Analysis of aircraft microphysical observations obtained during early 1987 was usually supportive concerning <br />cloud seeding potential, particularly in regard to a general absence of significant "ice multiplication." Ice <br />multiplication has been observed in some winter clouds; for example, over the Sierra Nevada of California <br />where large concentrations of ice particles often develop through microphysical processes. This often results <br />in efficient natural conversion of cloud liquid water to precipitation and little or no cloud seeding potential. <br />It is known that cloud droplets larger than about 24 micrometers in diameter need to be present in <br />significant concentrations as one condition of an important ice multiplication process. However, the Arizona <br />cloud droplets were rarely that large, suggesting that ice multiplication by that process should be infrequent. <br /> <br />Measurements of ice particle concentrations were examined from the many aircraft missions over the <br />Mogollon Rim. The median concentration was about 1 per liter with most values between 0.1 and 10 per <br /> <br />v <br />