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25 As thi sounding becomes neutrally stable (Fig. 3.3b), a weak convergence zone develops which results in additional vertical displacement of the air- flow. Liquid water contents of 0.2-0.3 g/m3 are typical under these condi- tions. In both the stable and neutral stages, gravity waves are commonly superimposed on this structure. (22 Harch, flight 1, is a good example of the neutral case). As more instability develops the convergence zone becomes associated with a convective region upwind of the mountains (Fig. 3.3c). The liquid water produced in the convective region apparently feeds into a more general liquid water region over the mountain, and produces the highest liquid water contents found in San Juan storms. (29 December is an example.) The rate of lifting, and therefore the rate of condensation of liquid \"rater, increases \'1i th increasing ins tabili ty. This suggests that a higher ice crystal concentration is required to efficiently convert the liquid to precipitation under unstable conditions. Relatively low ice crystal con- centrations suffice to glaciate the cloud under stable conditions. Crystals falling to the mountain must fall through the liquid water region over and upwind of the mountains, and frequently reach the surface as moderately or heavily rimed crystals. Frequently, graupel showers are observed on the mountains. Particularly under unstable conditions, the high liquid water contents at heights of 1-2 km above the mountains indicate that significant quantities of liquid water are being lost from the precipitation that reaches the target area. For example, if a liquid water content of 0.5 g/m3 were converted to snO\,1 falling at I m/sec, a 2 nun/hr increase in the precipitation rate would result. This is t\vice the average precipitation rate in these stonns, and would be highly significant. I I I I I I I I I I I I I I I I I I I