Impact of Terrain Resolution on Precipitation Formation in a Simulated Orographic Cloud

Orographic precipitation is the primary water resource in the Western United States. Snowmelt from orographic precipitation in the mountains of Idaho powers over a dozen hydroelectric power plants and irrigates over 2 million acres of land. Although advances have been made in understanding orographic precipitation formation and associated cloud microphysics, investigations on the relationship between precipitation and complex terrain on a fine grid scale are still limited. This research aims to better understand the impact of terrain height on orographic clouds, and their subsequent precipitation formation, using a high-resolution simulation (900-m grid spacing) of the Weather Research and Forecasting (WRF) model. This modeling study is based on a case from the SNOWIE (Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment) field campaign that occurred on 31 January 2017. In this case, a shallow cloud formed with an abundance of supercooled liquid water and strong winds, which were over 33 m/s at around 4875 m. Modifications were made to the resolution of the WRF topography to explore the role of terrain on the formation of natural orographic precipitation in this case. The results of topography sensitivity tests will be described, including the dynamics, cloud fields, and precipitation from a control simulation (using default high-resolution terrain) and a sensitivity simulation with 20 times coarser resolution terrain data.