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I I I I I I I I I I I I I I I I I I I markedly, snowfall rates at TAR had decreased, and SL W depths had again increased. Although the rndar pattern by 1103 did not appear markedly convective, heavily Timed snow particles, including graupel, were observed at TAR. The final period of the field experiment is characterized by the PPl's in Fig. 51. Here echo coverage and intensity continued to decline. The echo pattern by 1306 had a much more convective appearance. The cloud field in general was apparently thinning as SL W depth also ,bl'fadually decreased from 1100 through 1400. After about 1230 the sno"fall rate at TAR dropped to less than 0.5 mm h-l, and breaks in lhe overcast were observed Satellite images revealed that a large area of colder cloud tops shifted somewhat south of the research area, leaving the Wasatch Plateau in a region of warm-topped cloud by 1400. The decrease in moisture was also seen in the rvtPA soundings which shO\ved a shallower saturated layer by 1400. __ az,.e?,..... ,,-, ~,.,.. ."R' 1(, u_, 1~ ~......., 11.' .''-''Mo....,,,... ....-... ..- ~..... t,_ n'._1\ '60.. II .'_' 1\ . ~'._' t11 ._........r~"t.. .-._.. .-. ..,.... .-" &. - , -" - -. ,w ~ - , -.. -- --. .. ..... '" .-.., ,~ . - ~ . '. ...._, '-'- - "' o~ - '" 0.- -.'. Figure 51. Radar PPl's taken at 1209 (Jejij and 1306 (right) on 7 February 199~. 3. Comparati\'e Radiometer .\Ieasurements Three measurement periods were selected for a data comparison between the DR! mobile radiometer and the USSR stationary radiometer. The USSR radiometer position at RRS was at the upwind edge of the top of the Wasatch Plateau, near the east-west location where air \\-'ould attain its maximum vertical displacement after being forced over the plateau by winds with a westerly comJXlnent. In the absence of precipitation this location would be expected to have the greatest SL W content. Huggins (1995) showed that the SLW depth maximum was, on average, slightly upwind 68