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2004 JOURNAL OF CLIMATE AND APPLIED METEOROLOGY VOLUME 22 as estimated from the radiosonde data available, had little if any association with suggested seeding effects. An attempt was made to test Grant and .Elliott's (1974) suggestion that cloud top temperature should be important in establishing the requirement for seed- ing in the BRE. Dual partitions were used such that only days with mean Ridge temperatures ~ -9.0oC were included and further partitioning was by cloud top temperature. The results of partitioning this pop- , ulation into halves, thirds and quarters are shown in Table 8. It can be seen that the lower half of the cloud top temperatures yielded relatively low probability values in Zones 1 and 2, while the warmer cases did not. The cases contributing to the low values appear to be con- centrated from approximately -38 to -280C. The mean double ratios associated with those probability values ~0.05 ranged from 1.54 for all 84 cases in Zone 1 to 2.41 for the second coldest quarter in Zone 1. This does not support the notion that cold cloud tops, with presumed naturally high ice crystal concentra- tions, reduces or eliminates seeding potential near Bridger Range mountaintop levels. It is worth recalling that the Bridger Range rises abruptly and is a rather narrow barrier (see Fig. 1). Ice crystals formed high above the surface would be expected to have greater influence on broad barriers where the crystals would more frequently have suffi- cient time for settling to the surface before being trans- ported beyond the barrier. d. Partitioning by 500 mb temperature The temperature at 500 mb has been used to par- tition a number of winter orographic cloud seeding projects, often with the assumption that it is an ap- proximation or index of cloud top temperature. The Climax experiments are a notable example of appar- ently successful partitioning by the 500 mb temperature (Mielke et al., 1981a and Mielke et al., 1982). The BRE was also partitioned by this parameter because of its widespread usage. Once again, all available local sounding data were averaged to estimate the daily 500 mb temperature. The median value for the entire population of 152 days was -260C, and 80% of all daily means were between -19.5 and -34.50C. The Wilcoxon test was applied to the entire population, and halves, thirds and quarters of it, for the three zones of Fig. 1. Only one of the resulting 30 probability values was ~0.05, which could be expected by chance. Therefore, partitioning the BRE data by 500 mb temperature alone did not suggest any changes in snowfall associated with seeding. e. Partitioning by 700 mb wind speed The component of the horizontal wind speed per- pendicular to the Bridger Range might be expected to be quite important to the precipitation process, both for natural and seeded storms. Hill (1980a) argues that the cross-barrier flux of supercooled water is approx- imately proportional to the square of the cross-barrier wind speed. Further evidence to support this concept is given by Hill (1982). In addition, the. amount of time available for ice particle growth and fallout at any downwind distance is largely dependent upon the cross-barrier wind speed. The eastward component of the 700 mb wind speed was chosen to approximate the cross-barrier wind speed. This quantity was calculated for each available rawinsonde observation and the average of all available observations was used to partition each 24 h experi- mental unit. The entire population of 148 experimental days with a measured positive eastward component of 700 mb wind speed was subdivided into halves, thirds and quarters. These and the whole population were tested by the Wilcoxon test for Zones 1, 2 and 3 of Fig. 1. Of the resulting 30 values of Wilcoxon probability, only one was ~0.05. This is about what one would expect by chance indicating that normal wind speed alone was not strongly associated with suggested seed- ing effects. This should probably not be a surprising , TABLE 9. Ridge temperature partitions for colder days using the single Gallatin Range gage for control. Probabilities and double ratios (DR) are for 3 zones of Fig. 1. Experimental days Zone I Zone 2 Zone 3 Range (0C) All s/ns* W** MRPP D.R. W MRPP D.R. W MRPP D.R. ~ -7.0 131 65/66 0.08 0.09 1.34/2.67 0,20 0.10 1.11/2.10 0.28 0.26 1.16/4.20 ~ -9.0 100 44/56 0.06 0.09 1/51/1/65 0.11 0.10 1.33/1.87 0.11 O.ll 1.39/4.30 ~ -11.0 68 31/37 0.08 0.08 1.34/1.66 0.25 0.34 1.42/1.66 0.11 0.16 1.52/4.50 ~ -13.0 49 22/27 0.05 0.03 1.50/3.62 0.02 0.02 2.31/5.24 0.04 0.05 2.55/9.17 ~ -15.0 26 10/16 0.30 0.25 0.95/0.86 0.11 0.17 1.82/2.04 0.05 0.06 1.87/5.71 * s-seeded/ns-nonseeded, ** Wilcoxon.