The Wyoming Winter Orographic Cloud Seeding Program (Wwmpp): Program Overview and Design Aspects in Its Evaluation

In 2005, a feasibility study was completed, which among other aspects, outlined a pilot program for operating and evaluating a winter cloud seeding project for enhancing snowfall in two mountain regions of Wyoming. The Wyoming Weather Modification Pilot Program (WWMPP) was developed and carried out over a 9-year period, with two seasons of preliminary studies, one initial seeding season, and six seeding seasons under a refined experimental design. The main goals of the WWMPP were to establish an orographic cloud seeding program in the two areas of interest encompassing three target areas (the Medicine Bow Range, Sierra Madre Range and Wind River Range) and evaluate the feasibility and effectiveness of the cloud seeding. The WWMPP built off of results from the feasibility study and those of past research on winter orographic cloud seeding that established and refined a generally-accepted cloud seeding conceptual model. Two general approaches guided the evaluation of the WWMPP: a) a randomized experiment that built distributions of seeded and control (unseeded) cases, and b) exploratory studies that investigated a variety of ideas on aspects of the conceptual seeding model, including physical studies and model simulations.

In this presentation, we provide an overview of the structure, operation and evaluation of the WWMPP and its evolution over the 9-yr period. This establishes the context for several other conference presentations on WWMPP results. Also described are elements of the final experimental design, both logistical aspects and the statistically design, with a discussion of the strengths and weaknesses in the experimental design.