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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />- <br /> <br />... <br /> <br />- 97 - <br /> <br /> <br />lower level stratus and stratocumulus. <br /> <br />When cloud top temperatures are below about -8 and -12oC the following ice <br /> <br />particles are observed in the orographic clouds (listed in order of <br />predominance): irregular plate-like crystals, irregular particles, hexagonal <br /> <br />plates, crystals with broad branches, sectored crystals, stellars, dendrites, <br /> <br />and bullets. For cloud top temperatures above about -8 to -120C the predominant <br /> <br /> <br />ice perticles are irregular, warm columns, needles and sheaths. ~fuen <br /> <br /> <br />convective clouds are present frozen drops, often in groups, are common. On <br /> <br />the eastern slopes of the Cascades a larger proportion of the ice particles are <br /> <br />irregular in shape and the particles are frequently rounded rather than angular, <br /> <br />indicating that they are evaporating. Needles and sheaths are rarely observed <br /> <br />over t~e ea8tern slopes. <br /> <br />I <br /> <br />.... <br /> <br />Fig. 4.1 and Fig. 4,2 show isop1eths for the average liquid water content <br /> <br /> <br />across the Cascade Mountains from measurements obtained with the Johnson- <br /> <br /> <br />\Hlliams meter. These curves are based on measure::ients made dUj:,ing s;.;;ven <br /> <br /> <br />flights (Jan. 8, Feb. 3, 18, 22, 25, r1arch 28, and April 1, 1971) in which the <br />prevailing "rind was i.n the quadrant SW through NH. Three of the flip,hts were <br />. I <br />in p~e-frontal situations, one in a post-frontal situation, in two cases a front <br />passed over the Cascades during the flight, and in the other flight there was <br /> <br />a north-westerly airstream over the mountains. It can be seen that, on average, <br /> <br />the liquid water content reaches a peak value at about 13 nautical miles west <br /> <br />of the CascaGe divide and a minimum value at about 15 miles east of th~ divide. <br /> <br />(N.B. Peak values of the liquid water contents are, of course, much higher <br /> <br />than those shown in Fig. 4.1 and 4.2.) <br /> <br />, <br />I <br /> <br />I <br /> <br />- <br /> <br />I <br /> <br />- <br /> <br />I <br />I <br />I <br />I <br />