The Weather Bureau ACN Project

Abstract

The Weather Bureau has completed a field program in western Washington to investigate the applicability of cloud seeding techniques in migratory cloud systems associated with middle latitude cyclonic activity. The project was designed to give statistically valid estimates of the effects of seeding with dry ice from aircraft, as well as affording surveys of cloud structure with particular reference to natural precipitation mechanisms and seeding potentialities. A number of statistical evaluations have been carried out and, considered as a whole, do not show significant results from the seeding. However, because of the margin of uncertainty present, none of the evaluations excluded the possibility of limited effects. The cloud surveys suggested that favorable seeding opportunities were somewhat infrequent due to the abundance of natural ice crystals in the deeper cloud layers.