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occurred which limited the aerial operations to seven rather marginal bandswhile the biulk of the seeding was conducted in the same manner as the previousthree years.WORK PERFORMEDThe 1970-71 fiold program began November 1, 1970 and continued throughApril 1971. There were several good seeding opportunities during November andDecember, but the remainder of the season was relatively dry with only minorseeding opportunities. The storms after mid-December were characterized by coldair masses and generally light precipitation.A total of 2.) bands were declared operational during the 1970-71 season.Twenty-two of these were treated by the ground seeding mode - 13 seeded and ninenot seeded, and seven by the aerial seeding mode - three seeded and four notsZeeded.After four years of pyrotechnic seeding from a single ground location, atotal of 107 bands have been identified and declared operational. Fifty-six ofth••e bands were seeded and :1 not seeded.MODEL COMPUTATIONSkawinsondes were taken just prior to the entrance of th, bands into the testreair. In order to make quantitative use of this abundant air mass and wind datafor ,lucidating the obsenred patterns of seeding effect, use was made of the Areaof Effect morel (Elliott, 1969). This model has been specifically developed forp-edictingf the area of effect due to the seeding of winter storms over an orographicbarrier under both stable an6 unstable air mass conditions. As appliedhere, only the unstable case is used. The model considers the barricr configuration,the intlowing air majss structure as given by a sounding, and the location,streu;ith, and typo of the artificial nuclei source.The model is steady state and Lagrangian in character. It predicts themovem, nt and dispersion of the nucleant, its entrainment into convection, andthe production of ice paii-titles by nucleation, their growth by diffusion andaccretion ;as the% as c(.nd in convection, and their drift during fallout fromtilted conv'ecttiol colulm:.ý.The area of' eet model omploy., a1 parameterized torm of colnvectionz howr,adynamice c:l.vection model using the same ice phase nucleation all(d growth-0-{-