Cloud and Precipitation Analysis of Natural and Seeded Snowfall in the Payette Mountains of Idaho

Natural cloud composition and variability can have a significant impact on the effectiveness of cloud seeding at enhancing snowfall over complex terrain. In theory, cloud seeding with silver iodide can increase the effectiveness of snow growth and fallout in clouds containing supercooled liquid water due to low natural abundances of ice nuclei. Ice initiation and ice growth (liquid and ice water content, cloud droplet concentration, ice particle habits), and variables relating to snow growth/fallout were captured extensively throughout the Seeded Natural and Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) field campaign in the Payette mountains of Idaho between January and March 2017. SNOWIE utilized ground-based dual-polarization radars, airborne in-situ cloud droplet probes, and an airborne vertically-pointing Doppler radar to capture natural and seeded orographic clouds. In addition to a research aircraft, which flew parallel to the prevailing wind to capture downstream vertical velocity, reflectivity cross-sections, and the overall evolution of natural and seeded clouds and precipitation, there was also a seeding aircraft, which flew in a perpendicular flight path further upstream of the study region and released ejectable and burn-in-place silver iodide flares to disperse seeding material. In this study, we compare environment conditions, cloud structures, and precipitation growth in all 24 intensive observations periods (IOPs) from SNOWIE. We analyze ground-based radar and in-situ observations together with airborne in-situ and radar measurements to qualitatively differentiate the evolving snow growth and fallout processes within natural and seeded clouds. To incorporate the impact of seeding, the amount of seeding material released, and the seeding time/duration is included in these analyses. Preliminary results show that IOPs with abondance amount of supercooled liquid water, deficient natural ice, and warm cloud tops are the cases where seeding has shown to be successful, and that diffusional growth can be linked to enhancement of surface snowfall.