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<br />SECTION I <br />INTRODUCTION <br /> <br />The CRADP (Colorado River Augmentation Demonstration <br />Program) has three main objectives: (1) to investigate and <br />improve cloud seeding technology as it applies to the Col- <br />orado River Basin, (2) to improve the cost-benefit ratio of <br />the technology, and (3) to refine the suspension criteria. <br /> <br />1.1 Choice of Grand Mesa <br />Experimental Area <br /> <br />The Montrose Skywater Office was established in August <br />1983 to serve as the base for field activities on the Grand <br />Mesa in west-central Colorado. The Grand Mesa was selected <br />as the primary experimental area for CRADP after an ex- <br />tensive site selection process that has been documented in <br />several Bureau internal memorandums during early 1982, <br />and summarized in a memorandum by Super [1]1. The pri- <br />mary attributes of Grand Mesa as an area for applied research <br />into winter orographic storms and their modification are: <br /> <br />a. Grand Mesa is a reasonably large area with a significant <br />seasonal snowpack that produces runoff into the Colorado <br />River. <br /> <br />b. There is excellent access to the top by an all-weather <br />road, and good over-snow access around the area due to <br />the relatively flat terrain. <br /> <br />c. There is a high frequency of winter storms from all <br />important directions (southwest to west to northwest) due <br />to a significant rise above upwind terrain, and lack of <br />"shadowing" by upwind mountain barriers. <br /> <br />d. There are two adequate airports within less than 30 <br />minutes flying time that are only infrequently closed by <br />weather. <br /> <br />e. Grand Mesa has a relatively uniform terrain at high <br />altitude, 3000 to 3400 m, which permits aircraft sampling <br />within 300 m of highest terrain_ <br /> <br />The choice of Montrose as the base for CRADP field activities <br />was due to its proximity to the Grand Mesa, and because it <br />has a suitable airport and adequate facilities and services for <br />the field operations_ While the road distance to the top of <br />Grand Mesa is essentially the same from Montrose or Grand <br /> <br />'Numbers in brackets refer to entries in the Bibliography, section 8. <br /> <br />Junction (either of which would be a suitable base), the road <br />from Montrose offers better winter travel with fewer switch- <br />backs, less avalanche hazard, and a southern exposure that <br />results in more frequent melting of snow and ice on Highway <br />65. <br /> <br />1.2 Goals of Winter Field <br />Programs <br /> <br />The main goals of the winter field programs for January 1983 <br />through March 1985 were concerned with the "seedability" <br />of clouds over the Grand Mesa. It is well known that a nec- <br />essary, but not sufficient, condition for winter orographic <br />clouds to have seeding potential is the presence of SL W <br />(super-cooled liquid water) e.g., see Grant and Kahan [2]. <br />More precisely, the SLW must exist over the mountain barrier <br />to at least the lee side where downward airflow and asso- <br />ciatedevaporation often deplete the SLW.1f the SLW is <br />naturally converted to ice particles further upwind, the cloud <br />is probably already efficient in producing precipitation and <br />has no seeding potential. <br /> <br />The main questions that were addressed during the study <br />period were: <br /> <br />a. What are the spatial and temporal distributions of <br />SL W over the Mesa? <br /> <br />b. What are the natural ice particle constraints for <br />seeding, including their spatial and temporal distribu- <br />tions? <br /> <br />c_ How can the SLW region be appropriately seeded <br />when not efficiently converted to precipitation by na- <br />ture? <br /> <br />No cloud seeding was conducted during the study period <br />reported herein. The objective was to effectively marshal <br />available resources to better understand the seeding potential <br />of Grand Mesa winter clouds, and how to recognize and treat <br />that potential in future seeding experiments. <br /> <br />1.3 First Winter Season <br /> <br />The initial exploratory field program on Grand Mesa took <br />place from mid-January to mid-February, 1983. Bureau of <br />Reclamation personnel were temporarily assigned to the <br />