Assessing and Validating Cloud Seeding Plume Targeting Using a High-Resolution WRF Model, a Dispersion Model, and Snow Trace Chemistry

The Truckee River Watershed drains a 100-km long section of the eastern slopes of the northern Sierra Nevada Mountains in California and Nevada. Snowfall from the watershed and nearly 1 million acre-feet (123,000 hectare meters) of water storage provides much of the water needs of the Lake Tahoe region and the growing urban areas of northwestern Nevada. This watershed has had research and operational cloud seeding programs dating back as far as the 1960s. Over the past 5-years a network of 7 ground-based remote-controlled cloud seeding generators have been operated across the watershed.

For this study we study we developed a 1-km WRF post analysis numerical model centered over and upwind of the Sierra Nevada Mountain’s Truckee River Watershed. Several multi-day winter storms that occurred during the past five winters were modeled. The storms included periods associated with Atmospheric Rivers and periods associated with maritime polar air masses from the Gulf of Alaska. The storm periods are analyzed and the mesoscale and associated cloud microstructure are presented. Next, simulated silver iodide plumes are released from the generators using a Lagrangian Stochastic Particle Dispersion Model. The dispersion model is used to identify the geographic and storm locations were cloud seeding was active. Snow samples and snowflake images from the target areas were collected during these storms. The snow samples were analyzed for silver content using the Desert Research Institute’s trace chemistry lab, allowing the plume model to be verified. In addition, the snow crystal images collected will be compared to the WRF microphysical depiction of the co-located cloud structures.