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during their beginning and ending portions, usually associated with shallow clouds. An abundance of cloud liquid water was sometimes found during the middle portions as well, again often with shallow clouds. But important exceptions existed when cloud liquid water coexisted with moderate to heavy snowfall rates. Such cases had strong winds that apparently produced significant uplift over the mountain barrier, resulting in production of liquid water condensate at rates in excess of natural conversion to snowfall. Examination of cloud top observations by radar revealed that more than half of all 1987 hours with cloud liquid water were with shallow clouds extending no more than 2.5 kilometers above the Happy Jack site. But such clouds produced only 12 percent of the total precipitation during the field program. This suggests these clouds may be the best candidates for seeding. Considerable temporal variability in cloud liquid water amount was usually seen throughout the course of each storm. Time histories indicated rapid changes from periods with abundant cloud liquid water and little or no precipitation, indicating inefficient clouds, to very efficient precipitation producing clouds. Thus entire storm episodes cannot be thought of as simply seedable or nonseedable. Rather, the seeding potential of most storms varies considerably over relatively short time periods (hours) with portions appearing seedable and other portions appearing naturally quite efficient at producing precipitation. Further, while some apparently seedable (or nonseedable) periods last for several hours, others may be very brief. These temporal observations are based on radiometer measurements above a single site. Aircraft sampling revealed pronounced spatial variations of cloud liquid water as well. It is important that these results be incorporated into planning of future seeding strategies. It will be very difficult, and often impractical, to rapidly change the seeding treatment in response to the short-term changes in seed ability observed during most storm episodes. The only practical approach may be to seed throughout entire storm episodes, assuming that seeding during naturally efficient periods results in negligible reduction in snowfall. Some winter seeding projects in the western mountains of the United States have suggested this hypothesis is valid, but it should be tested in Arizona prior to operational seeding of entire storm periods. For the two-season data set, cloud liquid water was more commonly associated with stratiform clouds than convective clouds. However, because the difference was not great, both cloud types are important for cloud seeding potential. Most of the convection was embedded in general cloud layers and rather weak as indicatyd by visual observations and aircraft measurements of limited liquid water amounts. More vigorous convection was sometimes apparent, and occasionally thunder was heard. Isolated towering cumulus clouds occurred on some days, but their contribution to the radiometer-observed cloud liquid water was limited. In-depth analysis incorporating all available surface and aircraft data suggested that isolated convective clouds offer little winter seeding potential over the Mogollon Rim. The presence of cloud liquid water and occurrence of precipitation were quite dependent upon wind direction at both field locations. Southwesterly flow was most important at Happy Jack with northeasterly flow also significant. Westerly flow dominated the cloud liquid water and precipitation periods at Hannagan Meadow. In all these cases, the winds are generally perpendicular to the mountain barrier, thereby maximizing uplift of moist air and the resulting condensation into cloud droplets that was sometimes followed by snowfall. IV