Evaluating the Precipitation Impacts of Cloud Seeding in the Medicine Bow and Sierra Madre Ranges Using WRF-WxModⓇ within an Ensemble Modeling Framework

Precipitation and snowpack over the Medicine Bow and Sierra Madre Mountain Ranges directly affects water supply in the North Platte and Little Snake River Basins, thereby having far-reaching effects on agriculture/ranching, recreation, wildlife habitats, and the overall economy. With the goal of enhancing precipitation, the Wyoming Water Development Office (WWDO) has contracted with Weather Modification International (WMI) to conduct an aerial cloud-seeding program focused on the Medicine Bow and Sierra Madre Ranges since 2018. In order to evaluate and quantify impacts from the aerial cloud-seeding program, WRF-WxMod^Ⓡ and WRF-Hydro^Ⓡ were run over one winter season (2019-2020) in order to simulate the effects of cloud seeding with silver iodide (AgI) on clouds and precipitation as well as assess impacts on streamflow in basins over the experiment area.

The impact of cloud seeding on precipitation was simulated with a high-resolution (1-km grid length) ensemble modeling approach in order to estimate model uncertainty associated with natural and seeded clouds and precipitation. The ensemble configuration consisted of 36 members (12 control members + 24 seeded members), with stratifications by 1) large-scale forcing, 2) planetary boundary-layer scheme, 3) background cloud condensation nuclei concentrations, and 4) AgI activation rate and scavenging values within WRF-WxMod. This presentation will highlight key findings regarding impacts of aerial cloud seeding on precipitation over the 2019-2020 season, with a focus on using flight-level and ground-based observations to quantify additional precipitation provided by cloud seeding; associated cost effectiveness calculations will also be provided. A companion paper (Dougherty et al.) will present results focusing on simulating the impacts on streamflow in basins over the experiment area using WRF-Hydro.