WMOD00317

• Contract/Permit #: 14-06-D-6999
• Project Name: CAWRP
• Title: Cascades Atmosphere Water Resources Program - Volume I
• Prepared For: US Department of the Interior Bureau of Reclaimation
• Date: 7/1/1970
• Weather Modification - Doc Type: Report

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- 111 -

collected from the aircraft are also given in Section 4,

and the role of ice crystal fragmentation in clouds is
discussed.
Observations made at the ground stations in the Cascade

Project during the winter of 1970-71 are described in Section

5 and details are given on the types, sizes and character-

istics of the precipitation particles in different synoptic

conditions. The observations indicate that most of the

riming occurs below about 9,000 ft. and that riming is

heavier in post-frontal than in pre-frontal situations. The

degree of riming increases with increasing wind speed and

water content at the 10,000 ft. level. At the crest of the

Cascades the rate of precipitation increased with increased

riming but at stations on the eastern slopes the reverse

may hold. Stations on the west side of the Cascades generally

receive more precipitation than those on the east side but

this difference is usually much greater in post-frontal condi-

tions. Trajectories are deduced for the solid precipitation

particles in several situations. The smaller crystals often

originate 1n clouds situated many tens of miles upwind of the

point at which they eventually reach the ground. In the

presence of strong easterly winds near the surface, but

westerly winds at higher levels, the particles often originate

west of the divide, are carried across the divide, and then

return to near the divide on the easterly winds before

reaching the ground. Some implications of these results on