Ice-Phase Seeding Potential for Cumulus Cloud Modification in the Western United States

Abstract

A one-dimensional, steady-state cumulus model is used to evaluate the climatological potential for precipitation augmentation by ice-phase seeding of isolated cumulus clouds in the western United States using data for May-September 1967 and 1968. Atmospheric conditions favorable for seeding with ice nuclei in order to initiate thermodynamic instability occurred on approximately 25% of the days. On these days, the calculations indicated that seeded cumulus clouds could have been made to produce an average of approximately 50% (0.3 inch) more precipitation than their non-seeded neighbors. Decreases averaging approximately 0.1 inch per cloud were calculated to occur on approximately 20% of the days. The areas of the western United States that would have been most favorable for ice-phase seeding of isolated cumuli during the two years of the study were the southwestern states of Arizona, New Mexico and Texas. The least favorable areas were in the plains states of Kansas, Nebraska and South Dakota.