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I , , I I I , , I I I I I I I I I I I )~ - 95 - ice to water is less than in pre-frontal conditions and water droplets become increasingly common even at temperatures as low as -150C. At temperatures above about -BoC the clouds frequently contain only supercooled water. Between -8 and -14oC frozen drops, irregular ice particles, dendrites and stellars are found. Riming is common and graupel particles are collected on o~casions. In post-frontal conditions the majority of the more fragile star-like crystals are fragmented both when collected r~om aD aircraft and on the ground. Turbulence readings are much higher in post-fron~~l than pre-frontal conditions and the distributions of liquid water and ice particles are more variable. Interestingly, the degree of irregularity of the ice crystals appears to increase with increasing turbulence. A summary of the ccnditions in pre-frontal and post-frontal clouds over the Cascade Mountains is contained in Table 4.l. 4.1.3 Orographic Effect of the Cascade Mountains The effects of the Cascade Mountains on clouds in frontal situations have been mentioned above. In the absence of frontal activity, but with a strong westerly airstream, extensive orographic clouds form o~er the western slopes of the Cascades which can give rise to light but steady precipitation. These clouds are generally layered with the lowest layer extending from the tops of the mountains to about 8,000 ft, with further l~yers u? to l2,OOO ft and some- times higher layers. Clouds are thinner en the leeward slopes. There is often a thin haze of ice crystals which appear to originate from the denser clouds west of the Cascade divide. This haze is usually thin enough for the ground or sun to be seen through it. Water droplets predominate in the wave clouds,