Cold-season precipitation processes in shallow orographic clouds over a continental mountain range: impact of controlled ice nucleus injection

Orographic cloud and precipitation measurements were made during AgI Seeding of Cloud Impact Investigation (ASCII) campaign from January to March of 2012 over Sierra Madre Mountain range in southern Wyoming. Wyoming cloud radar (WCR) and Wyoming cloud Lidar (WCL) were mounted on the Wyoming King Air (WKA) with several cloud measuring instruments aboard the WKA and snow measurement instruments on the ground, including two Ka band profiling micro-rain radars (MRR), located upwind and on top of the mountain. A dual-polarization X-band Doppler radar performed volume and RHI scans from on top of the mountain. Soundings and profiling radiometers monitored the upwind environment. Orographic clouds appear to be remarkably efficient snow generators. This will be shown by means of an analysis of cloud top temperatures and WCR reflectivity profiles. Clouds in the free troposphere over land appear to require a lower cloud top temperature or greater depth to produce snow. Ice initiation mechanisms near the ground, such as blowing snow and ice multiplication on rimed canopy surfaces, combined with turbulent BL mixing, may be important in snow growth in orographic clouds. Our particular focus in ASCII is to examine whether ground-based ice injection (glaciogenic cloud seeding using AgI nuclei) can glaciate a supercooled cloud and initiate or enhance snowfall and suppress the cloud liquid water.