Trace Chemical Analyses of Snow during the WWMPP: Results and Implications for the Randomized Statistical Experiment

For the past five seasons (Water Years 2010-2014) of the Wyoming Weather Modification Pilot Project (WWMPP), the Desert Research Institute conducted sampling and trace chemical analysis of snow in the Medicine Bow, Sierra Madre and Wind River mountain ranges in Wyoming, as well as for a control site in Colorado's Park Range. The goal of the sampling in the Medicine Bow and the Sierra Madre ranges was to provide physical-chemical evidence that would specifically support the WWMPP Randomized Statistical Experiment (RSE), as well as the companion AgI Seeding Cloud Impact Investigation Study (ASCII), a two-year study led by the University of Wyoming. As such, both real-time in-storm sampling of snow and non-real-time episodic profile sampling of snow were conducted in the Medicine Bow and Sierra Madre ranges. In the Wind River Range, the goal of the sampling was to provide basic physical-chemical evidence of a seeding impact without the seeding operations being restricted by the tenets of the randomized statistical crossover design utilized for the RSE. As such, only snow profile sampling was conducted once/season for the Wind River range.

In this presentation we briefly summarize the analysis methodologies (the sampling methodologies are presented in a companion paper) and discuss the results of the trace chemistry analyses of snow for both the real-time and profile sampling campaigns in all three ranges. We will use the results in the Medicine Bow and Sierra Madre campaigns to draw inferences about the degree to which these analyses imply a seeding signature of significant extent to be useful in evaluation of the RSE and whether or not targeting was optimal for the WWMPP RSE operations. By contrast, we will use the results for the Wind River Range to draw inferences about the potential effectiveness of an operational seeding program in the future in the Wind River Range, given that such an operational program is planned for Water Year 2015 as a potential mitigation strategy to the current prolonged drought in the Colorado River Basin States.