Challenges in Simulating Orographic Precipitation in Natural and Seeded Clouds

There are known uncertainties in our understanding and ability to accurately simulate orographic clouds and precipitation, and these uncertainties impact our ability to evaluate the impacts of cloud seeding. Recent observational studies from the Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment (SNOWIE) project have demonstrated that seeding with silver iodide (AgI) produces ice crystals. In addition, recent research from SNOWIE and the Wyoming Weather Modification Pilot Program (WWMPP) has also shown that seeding generally increases the precipitation of orographic clouds. Nonetheless, uncertainties remain with respect to ice formation and the role of turbulence and aerosol on cloud droplet spectra in natural clouds. In addition, quantifying the exact seeding effect is a major challenge due to the complexity of natural clouds and precipitation, as well as due to uncertainties in our understanding of the dispersion and activation of AgI. New modeling capabilities have recently advanced our ability to simulate orographic precipitation and newly developed model parameterizations that simulate the physical effects of AgI seeding are promising methods for the future evaluation of cloud seeding. However, the aforementioned uncertainties still need to be addressed, especially if these techniques are to be useful for the evaluation of cloud seeding. This presentation discusses the uncertainties and outlines steps toward making progress to improve our ability to simulate orographic clouds and precipitation and the impact of cloud seeding.