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I I I I , I I I I I I I I I I I I I I - 93 - The occluded fronts which pass over Washington State are often in their dying stages. Consequently, only a limited amount of moisture is advected upwards. Thus from about 12,000 to 30,000.ft the dewpoint depression increases; at lB,OOO ft it llsually is' about 2 to 5oC. However, if the frontal system originates well to the southwest, water saturated conditions may extend up to 16,000 ftalthough this is not a common situation. At temperatures between 0 and -lOOC the types of ice particles collected from the aircraft varies with location. Over the Puget Sound the airflow is generally from the southwest and the air.is close to water saturation. Sub- water saturated, warm region, solid slender columns are C01'lDnon, but sheaths and needles are also co1l~cted. Over the western slopes of the Cascades the low level easterly winds are usually strong and produce drying conditions, but at a few thousand feet above the surface the air is moist and from the southwest. However, this water-saturated layer of air is only a few thousand feet thick extending up to about the -lOoC level. Solid columns and irregular ice particles ~e common in this region. . Over the eastern slopes of the Cascades, the low level easterly winds produce orographic clouds and water . saturated conditions. Needles, sheaths and. irregular ice particles are dominant in this region although solid columns are also observed. At temperatures between -10 and -20oC water saturation is not common in the pre-frontal por~ions of winter storms. Typical crystals observed are irregular ice particles, plates and sub-water saturated star-like crystals with broad branches and sector-like branches. However, over the Cascades the orographic effect occasionally produces ice crystals which have grown in water saturated air (e.g. dendrites)..