A transformational approach to winter orographic weather modification research

SNOWIE is a unique example of an integration of publicly funded and privately funded resources. This partnership resulted in the collection of a robust dataset available to both academic researchers and IPC that will provide the basis for innovative investigations on winter orographic cloud physics and the efficacy of cloud seeding. The partnership greatly enhanced both groups’ research opportunities without hindering the operational side of the IPC cloud-seeding program. Moreover, a substantial part of the project’s success is attributed to the strong collaboration with IPC staff, who contributed highly valuable local knowledge of the weather in the region toward forecasting for the project, as well as facilitated remarkable local area logistical support. SNOWIE’s unique approach capitalized on recent advances in meteorological instrumentation and numerical modeling, such as the WCR and AgI cloud-seeding parameterization, with an innovative plan to collect in situ measurements of the impacts of cloud-seeding material released from a seeding aircraft in a manner that resulted in unambiguous seeding signatures in radar reflectivity. A major success in SNOWIE was that seeding signatures were observed in multiple IOPs, allowing the impacts of seeding to be investigated in many scenarios and providing support for the interpretation that signatures in the data were indeed impacts from the airborne seeding. Detailed analyses are currently under way to determine if signatures are detectable in additional IOPs where natural background radar reflectivity features are already present. Key components of the experimental design that led to this success were 1) the location of the DOW radars atop an upwind ridge, which provided critical observations across the basin despite the complex terrain; 2) having one DOW dedicated to rapidly scanning RHIs parallel to the wind and along the UWKA flight track, which tracked fast-evolving processes; 3) flying the UWKA parallel to the wind with a vertically scanning cloud radar, allowing for in situ particle measurements and high-resolution radar depiction of the clouds; and 4) the use of airborne seeding, from which an unambiguous seeding pattern was dispersed. The data and results from SNOWIE will be instrumental in addressing the long-standing questions regarding the effectiveness of winter orographic cloud seeding to augment precipitation. A comprehensive evaluation of the effectiveness of cloud seeding is a multistep process that starts with affirming the physical chain of events due to seeding and ends with determining how much additional precipitation (or subsequent streamflow) can be gained by seeding over a watershed. The results from SNOWIE to date have demonstrated the first step (French et al. 2018), and future work utilizing SNOWIE data and the cloud-seeding parameterization aims to continue chipping away at these critical questions to quantify the impacts of cloud seeding.