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the experimental area. A limited number of physical case study experiments, which released either propane or AgI from HAS, showed obvious seeding effects at TAR. An icing rate sensor just upwind ofthe propane dispensers was used to initiate a 2 hour experimental block whenever SL W cloud was observed to exceed a threshold, A programmed data logger then made a 11102TO.W 111"25'30W 39'40'30"N TAR Target We"",er Ob.. and 20.c probe HAS Propane s.eders and weather Obs. TSO Icing Ob.. SIR Waather ObI. GSC Target GRO Target GTR Target GON Target GSO Target GNO Control 39"39'O"N 39"37'30'N 39"36'O'N 111 "27'O.W 111025'30W 111 "24'O'W 111"22'30"W random decision to seed either the first or second of the two 40 minute experimental units (EUs) within the 2 hour block, with the other unit receiving no seeding. The last twenty minutes of each hour were used as a buffer period, to minimize seeding contamination of any following nonseeded EU, The population of non seeded units (placebos) provided the basis of comparison for statistical testing of propane seeding effectiveness in increasing snowfalL 111"19'3QW 111"21'O'W 111"'9'30W 111.1S'O.W 3 . Kilorreters Contollllntelval200 1M...... " + 111"16'30"W 2 111 "18'O.W o J. 1 Figure I, Map of the experimental area and site locations for the Utah 2003-2004 randomized propane cloud seeding experiment. The contour interval is 200 meters. Experimental unit snow water equivalent (SWE) observations provided the ti::st variable for each EU. These data were obtained by high resolution digitized precipitation gauges. Times of estimated seeding plume (or placebo) passage over the TAR and each gauge were based on HAS and TAR wind speeds and a relationship developed from prior plume tracing experiments. Five gauges were located on the windward slope and plateal:l top along the expected plume trajectory. This network permitted investigation of seeding effectiveness by distance from about 2 to 6.5 km downwind of the HAS, One of the gauge locations, GRD, proved to be too windy for suitable observations as discussed in the two references, and will not be considered further, Control gauge GNO was also maintained on the plateau top, crosswind of the seeding plume. It was well-correlated with the remaining four target gauges. Measurements at GNO were essential to reducing the high natural variance (variability) in snowfall during statistical testing. Wind, temperature, icing which indicates SL W presence, and other observations were made at the HAS and TAR for the purpose of partitioning the precipitation data set into subpopulations for most ofthe testing. Some limited observations were made at stations SIR and T AO shown on Fig. I, but they had minimal impact on the statistical testing. For all practical purposes the map 3 ;~:oi.;d:Li,,'1i