Observations of mountain-top rime icing in Utah: implications for winter season cloud seeding

Abstract. The presence of supercooled liquid water (SLW) in winter orographic clouds has long been recognized as the pivotal (although not sole) requirement in glaciogenic cloud seeding operations for precipitation augmentation. To address this factor, a program of mountain-top measurements of rime ice accumulations in Utah is being implemented in support of ongoing operational winter cloud seeding projects. Data from three such measurement sites are undergoing analysis on a seasonal and case study basis. Preliminary findings are summarized. Using representative precipitation measurements, the apparent relative precipitation efficiency of storms and portions of storms has been estimated. In many cases, rather orderly transitions in apparent precipitation efficiency have been documented and periods of sustained inefficient precipitation production were noted. These and other findings indicate that the ridge-top SLW measurements provide helpful insights into seeding potential and can be useful in operational seeding opportunity recognition.