Microphysical Impacts due to Glaciogenic Cloud Seeding in Wintertime Orographic Clouds

Observations from the 2017 Seeded and Natural Orographic Wintertime clouds – the Idaho Experiment (SNOWIE) reported recently in the Proceedings of National Academy of Sciences (French et al. 2018) demonstrate the microphysical evolution within an orographic cloud region following the introduction of silver iodide. These data provide clear evidence that, under certain conditions, the natural development of precipitation can be altered through cloud seeding. However, the observations reported consist only of a few cases. Here we examine several other cases from SNOWIE for which clouds were seeded using silver iodide. We identify seeded regions by using a simple advection model to predict the location of seeding material within the orographic cloud. Microphysical characteristics of seeded regions as determined from in situ cloud probes and airborne and ground based radar are compared to characteristics from outside seeded regions within the same cloud systems. Here we report on similarities and differences between seeded and unseeded regions for a number of SNOWIE cases and a range of cloud conditions and comment on what cloud characteristics are most susceptible to glaciogenic cloud seeding.

French, J. R., K. Friedrich, S. A. Tessendorf, R. M. Rauber, B. Geerts, R. M. Rasmussen, L. Xue, M. L. Kunkel, and D. R. Blestrud, 2018: Precipitation formation from orographic cloud seeding. Proc Natl Acad Sci USA, 115, 1168–1173.