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, " 12 Plains (Tex, Dep, Water Resour., 1982), but there is not enough evidence to evaluate their suggestions. In any case, studies to identify criteria which would distinguish clouds that persist from clouds that do not would be worthwhile. We have already noted that mesoscale features control the organization and size of convective clouds and, hence, the rainfall they can produce. One encouraging finding from the Texas HIPLEX work is that the mesoscale features controlling convection can be identified. Rawinsonde networks with spacings of 200 km have been found adequate to locate mesoscale features associated with heavy convective outbreaks. The mesoscale features can be identified objectively by computer analyses using filter techniques (D. Matthews, private com- munication,1982). An ability to identify and follow mesoscale features opens up many pos- sibilities in future cloud seeding experiments. For one thing, it would be possible to concentrate seeding experiments upon clouds in regions favoring further growth, rather than upon clouds destined to disappear a few minutes after their selection as test cases. The ability to measure mesoscale conver- gence would also provide an estimate of what the clouds would have done in the absence of seeding, thereby sharpening the statistical analysis. Continued attention to numerical modeling, including simulation of seed- ing effects, should improve our understanding of possible physical mechan- isms linking seeding to precipitation at the ground. Present indications are that the effect of seeding varies greatly among individual clouds, which is one likely reason why many statistical experiments have not been conclusive. It is not likely that two- or three-dimensional models could be run in real- time as an aid to cloud seeding operations, but it is reasonable to suppose that long-term modeling efforts will improve the physical hypotheses and thereby help in the design of future experiments. ACKNOWLEDGEMENTS The author wishes to express his appreciation to Dr. Bernard Silverman, Dr. Arlin Super and Mr. David Matthews of the Bureau of Reclamation for stimulating discussions and to Drs. Paul Mielke and Ken Berry of Colorado State University, for providing the P-values in Table V. REFERENCES Braham, R.R., Jr., 1981. Designing cloud seeding experiments for physical understanding. Bull. Am. Meteorol. Soc., 62: 55-62. Braham, R.R., Jr., Battan, L.J. and Byers, H.R., 1957. Artificial nucleation of cumulus. clouds. In: Cloud and Weather Modification. Meteorol. Monogr. 2(11), American Meteorological Society, Boston, MA, pp. 47-85. BuREC, 1979. The Design of HIPLt.i:X-1. Rep., Division of Atmospheric ResouctJ Re- search, Bureau of Reclamation, U.S. Department of the Interior, Denver, CO, 271 pp. Coons, R.D. and Gunn, R., 1951. Relation of artificial cloud-modification to the produc- tion of precipitation. In: T.F. Malone (Editor), Compendium of Meteorology. Ameri- can Meteorological Society, Boston, MA. pp. 235-241.