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23 3,4 Modifications of Method Due to the Field Data As noted previously, less than ideal field locations of the radio- sondes require modifications in the method or the assumptions behind the method. Minturn and Camp Hale locations require the modifications in determining the water balance, cloud efficiencies and trajectories. Ideally, the upwind station must be located upwind of the cloud. Minturn's balloons, however, passed through the cloud. In the analysis the assumption is made that the amount of cloud water advected is small compared to the vapor advected (about 1 gram of vapor compared to less than .1 grams of liquid and solid water per kg. of air (L.O. Grant, personal communication) and can be neglected. This small error results in an underestimation of precipitation because Fairplay, during the time of the experiment, was not cloudy. Balloon ascents from the Camp Hale site cause some problems. Be- cause Camp Hale's balloons do not sample the air at its highest point, but considerably upstream of that location, the high point of the tra- jectories must be subjectively decided. For the lower air, the crest of flow is assumed directly over the ridge line with the crest of flow of the higher air following a slight negative slope (Scorer, 1967). A third modification required by the non-ideal placement of radio- sondes is the computation of downslope evaporation. Between Camp Hale and Fairplay the air parcels ascend until they are roughly over the top of the ridge and descend past the ridge. While the parcels are ascending condensation takes place but during descent only evaporation occurs. The water balance includes both these stages. To get the total net condensation over the experimental area the water vapor added to the