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23 B. Microphysical Characteristics The microphysital observations in these storms yielded several surprising results. Supercooled water regions were less extensive than anticipated, and ice crystal concentrations were unexpectedly high. 1. Liquid water observations In most of the clouds studied, liquid water was found in three general regions: (a) over and slightly upwind of the mountain barrier; (b) associated \vith the upwind rise in the terrain near Navajo Reservoir, approximately 60-70 km upwind of the mountains; (c) associated with convection in a region approxi- mately 15-20 km upwind of the mountains. a. Reiion over and slightly upwind of the mountain barrier This region \vas the most common liquid water feature of these storms. It frequently extended about 10 km ahead of the mountains, and was produced by lifting of the air as it passed over the mountain range. More liquid water developed and the region was more widespread during unstable storm periods (such as 29 December flight 1, or 29. January flight 2); liquid \vater was absent or barely detectable during most stable stages (such as 30 January flight 1). The highest liquid \vater contents of the San Juan storms were found in this region. Supercooled water must be present also at considerably lower levels, since lifting of ~l km is required to develop liquid water content of 1 g/m3 in these clouds. Under stable conditions this liquid region probably merges with, and has its origin in, the convective region ahead of the mountains. Fig. 3.3 shows the nature of the liquid water region ahead of the mountain, under stable, neutral and unstable conditions. A feature of the airflow in the stable storm stage (Fig. 3.3a) is the blocked flow, which reduces the deflection of the airflow due to the mountain and causes less liquid water to be produced in the cloud. this case.) (30 January flight l"is a good illustration of I. I I I I I I I, I I I I II I I I I I I