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o ('lO2 2!, 4.3 Differences Between Experimental Areas In most significant respects, the two study areas are similar for purposes of experimentation. Each barrier rises over a kilometer above it.<; upwind valley, is over 20 km wide, and has a maximum elevation of about 3.4 km. Accordingly, the experimental design will be written for a single area, and the discussion in this section and in section 5 will apply to both the Grand Mesa and the Wasatch Plateau. Similar experimental designs will provide replication of results, an approach commonly used to test the plausibility of experimental findings. The application of the design will differ somewhat between the barriers, because of the operational differences to be noted. Future field operations plans will deal with these dissimilarities_ The two mountain barriers have a number of differences, the most obvious being their orientation. The Wasatch Plateau is a north-south oriented barrier. The crestline of the Grand Mesa lies approximately east-west. However, on both barriers the terrain influences the low-level flow which tends to turn perpendicular to the barrier crest (upslope). Significant SLW production has been observed over both barriers with large-scale flow between south-southwest and nDrthwest_ The difference in crestline orientation is not expected to significantly affect cloud responses to seeding. Three other significant differences exist between the experimental areas. First, the Wasatch Plateau has an excellent all-weather highway system, which will permit on-top, cross-plume sampling of AgI, tracer gas, and ice crystals by an instrumented four-wheel drive vehicle. Highways do not cross over the eastern portion of the Grand Mesa but do reach well up it.<; slopes. OversnDw travel is required to reach and traverse the Mesa top, and such travel is " practical as the terrain is not rugged. An instrumented DversnDw vehicle will be used for cross-plume sampling on the Mesa. However, large Dversnow vehicles are slow, and surface vehicle sampling clearly will playa larger role on the Plateau because of it.<; highway system. F Second, a WSR-88D advanced Doppler weather radar is scheduled to be installed on top the Mesa in September 1995, near it.<; northwest end. This radar will be part of the NEXRAD (Next Generation Weather Radar) network now being established nationwide for the National Weather Service and other agencies. Transmission of WSR-88D measurement.<; by radio for real-time use in the CREST operations center and recording for later analysis should be possible, which would eliminate the need for the program to operate a sophisticated surveillance radar on the Mesa. Some cost.<; would be incurred in obtaining the WSR-88D observations, but a significant net savings would result. This savings would be partially offset, however, by higher travel costs on the Mesa caused by more DversnDw travel. WSR-88D unit.<; scheduled for Utah will be too distant to serve a similar function for the Wasatch Plateau. The third noteworthy difference is that an upwind barrier, the San Pitch Mountains, lies parallel to the Wasatch Plateau at about 30 km distance (about 1.5 h travel time with typical winds). Seeding the Plateau from near the top of the San Pitch Mountains may be feasible, and that possibility will be tested during the direct detection phase. Seeding from the upwind barrier would provide considerably more time for AgI dispersion, and more time for ice crystal growth and fallout, two significant advantages. 20