Microphysical Characteristics and Evolution of Seeded Orographic Clouds

Supercooled liquid in orographic wintertime clouds can be converted through seeding using silver iodide (AgI) into ice particles, which subsequently can fall out as snow. In this study, ice and snow production is quantified and linked to environmental conditions and terrain for three days in January 2017, when orographic clouds in the absent of natural precipitation were seeded with silver iodide (AgI) in the Payette basin of Idaho during the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE). Airborne in-situ and cloud radar Ka-band observations are used to quantify supercooled liquid prior to injecting AgI into the clouds and ice nucleation as a result of cloud seeding. Dual-polarization radar observations from two ground-based dual-polarization precipitation X-band radars are used to determine microphysical processes. Preliminary results indicate that snow can fall out as quickly as 30 minutes after cloud seeding during strong (30 m s-1 at seeding level) wind conditions or can remain in the area for up to 90 min during weak winds (10-15 ms-1). Enhanced orographic lift and enhanced dendritic growth resulted in higher accumulated snowfall in particular over higher terrain. In addition, spatial and temporal evolution of supercooled liquid, wind shear, and the amount of AgI determine how much snow will be generated.