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Grand Mesa area to take observations. Most pertinent data ' were obtained with the University of North Dakota's Citation II instrumented aircraft based at Grand Junction Airport. Some ground instrumentation was also employed. The pri-. mary ground system was the recently acquired Bureau mi- crowave radiometer, which was operated next to Alexander Lake Lodge at 3115-m elevation at latitude 30002'31''N Ion; gitudeJ07057'50"W (see fig. 1-1). This was the only available high altitude site, at the time, with road access and com- mercial electrical power. While interesting data were obtained which documented the frequent occurrence of SL W, the site was not representative for northwest flow because of sub- sidence and cloud evaporation. Other ground instrumentation included precipitation gauges at two sites and a single hygro- thermograph, and time-lapse cameras at four sib~s. Occa- sional snowflake replicas were also made. Other supporting information includ~d twice daily NWS (National Weather Ser- vice) rawinsondes launched at Grand Junction airport, weather maps, and satellite photographs. ; The 1983 CRADP Data Inventory summarizes all data col- lected on the surface and by aircraft during the initial field program. Appendix A of that document contains the Site Director's Log, which discusses' daily activities and initial impressions from aircraffrilissions. The most important find- irig from the exploratory field study was that SLW frequently existed across the entire Mesa, which suggests that clouds were often seedable. 1.4 Second Winter Season After four Bureau personnel were transferred to Montrose in~ugustJ9~3, preparations began for the second CRADP field program, which took place on the Mesa from early November 1983 through March 1984. The same Citation II instr\Jmente~aircraft was used from late November to late DI'!~en)b!!r, and was based at Montrose Airport. The Bureau's microwave radiometer was available during November and December, and was , operated above the north shore of Island Lake at 3170-m elevation at latitude 39002'15"N, longitude 108000'17"W (see fig. 1-1). This po- sition was 120 m below and about 300 m south of the edge of Grand Mesa caprock. A position on top of the Mesa would have been more desirable because some subsidence and evap- oration of cloud liquid water was anticipated with northwest- or north-flow over the Island Lake site. However, practical considerations involved with mid-winter transport of the ra- diometer to the California field program precluded using an on-top site. The site used was considerably more represen- tative of the Mesa top than the site used during the initial field program. The Skywater SWR-75, 5.4-cm radar was collocated with the microwave radiometer. The radar was operated in a ver- tically-pointing mode to obtain cloud top observations from late November through March. Unfortunately, false returns were obtained in about the lowest kilometer above the radar, even during clear weather. This problem, apparently inherent in the system, reduced the value of the observations during periods with shallow clouds. A PMS, 2D-C ground station was operated during a single November and several December storms at the Island Lake site. The aspirated probe produced 20 images of ice particles plus size and concentration observations. Several of the sam- pling periods were coincident with aircraft sampling above the Mesa. '-I ! The GMO (Grand Mesa Observatory) was established prior to November, 1983, on top of the Mesa at 3290 m elevation at latitude 39002'54''N, longitude 1080Ol'15'W. The GMO was sited near an existing microwave' tower where commer- cial power was available. Winter access was by snowmobile from Highway 65, about 3 km west of the GMO. Routine observations at this site included wind speed and direction, 16 m a;g.1. (above ground level); air and dewpoint temper- ature, 5 m a.g.l.; and icing with two Rosemount probes,S m a.g.1. Time-lapse photographs of general weather condi- tions were also taken. Precipitation gauges were operated at four sites during the 1983-84 winter, including one on the upwind Uncompahgre Plateau. Several different gauge types were intercompared to determine which one was the most satisfactory for use on the Mesa. Several snowboard samples were also made to compare snowfall at different positions in a sheltered clearing, and to compare gauge catch with snowfall on the surface. 1.5 Third Winter Season The third field season on Grand Mesa was conducted from early November 1984 through March 1985. A microwave radiometer leased from Utah State University was operated at the Island Lake site during January through March; system problems prevented data collection prior to that time. A Ka- band, 0.86-cm radar, also leased from Utah State, was op- erated at the same site from mid-November through March. Both systems were operated in a vertically-pointing mode. No aircraft observations were obtained during the 1984-85 winter. ..j 1 I A heated anemometer and wind vane, and a Rosemount icing probe, were located about 70 m a.g.1. on the large microwave tower near the GMO. Air and dewpoint temperature were again monitored at 5 m a.g.1. at the GMO, and pressure data, measured by a Setra pressure transducer, were recorded at the GMO. The precipitation gauge network was expanded to six sites. Each site was equipped with a 45.5-cm-diameter orifice 2