The WWMPP builds off of past research into winter orographic cloud seeding that established and refined a generally-accepted cloud seeding conceptual model. Two general approaches are guiding the evaluation of the WWMPP: a) a randomized experiment that builds distributions of seeded and control (unseeded) cases, and b) exploratory studies to investigate a wide variety of ideas on detecting seeding effects, including physical studies to document the precipitation formation events hypothesized to be important to snowfall production in orographic storms. In this paper, we focus on the design aspects of the randomized experiment.
The first two winter seasons of the program (2005-06, 2006-07) were needed for performing exploratory studies to develop the evaluation plan, permitting activities, installing equipment, and peer review of the scientific experimental design. The initial seeding season (2007-2008) revealed some design issues that were subsequently addressed. Two seeding seasons under the experimental design have been completed. Elements of the final experimental design, both logistical aspects and the statistically design, are detailed in the paper. Some physical measurements are presented that describe the Wyoming program in the context of the conceptual model. Preliminary results will be presented to highlight strengths and weaknesses in the design and to report on progress to date.