Spatiotemporal Evolution of Seeded Orographic Winter Clouds Using High-Resolution Radar Observations

While the physical process is well understood by which silver iodide (AgI) introduced into a supercooled cloud produces ice crystals, the impacts of cloud seeding on cloud formation and evolution in orographic winter storms and the amount and spatial distribution of snow is still difficult to quantify. Many microphysical, thermodynamic, and kinematic factors can influence the cloud formation and the amount of snow that reaches the ground. We use observations from two ground-based dual-polarization scanning X-band Doppler radars to analyze the temporal and spatial evolution of seeded and natural clouds. The environment in which they form and evolve will be described through data from soundings and microwave radiometers. The data were collected during the 2017 Seeded and Natural Orographic Wintertime clouds—the Idaho Experiment. Out of the 20 cases where AgI was injected into supercooled liquid clouds, three cases show strong evidence of seeding signatures. Microphysical and dynamical processes within these seeded clouds were analyzed using vertical cross sections of radar observations at high temporal resolution combined with high-resolution volume scans as the seeded clouds evolve and snow fell out over the higher terrain. The analysis of dual-polarization parameters over 90 minutes shows the growth of ice crystals from moderately rimed particles to larger crystals that fell to the ground. Dual-polarization signatures of surrounding clouds, that were not seeded with AgI, will be compared to signatures found in seeded clouds.