Orographic influences on Great Salt Lake-effect snowstorms

In northern Utah, several mountain ranges surround the Great Salt Lake (GSL), a meso-β-scale saltwater lake associated with multiple GSL-effect (GSLE) storms each year. Past research has emphasized the importance of orography in the evolution of GSLE events, but the relevant physical processes have not been identified. This study examines the influence of orography on one lake-effect event and one lake-enhanced event associated with the GSL, through analysis of observations and numerical model sensitivity studies. Both events involve synergistic interactions between lake-effect and orographic processes, and show a dramatic decrease in precipitation intensity and coverage when either the lake or terrain forcings are removed. A foehn-like flow over upstream orography reduces the relative humidity of the incipient low-level airmass and limits the intensity of both events. A convergence zone in the lee of isolated upstream topography is positioned over the north arm of the GSL, and may play a role in organizing the 27 Oct 2010 lake-effect band. Downstream orographic influences are large in both events, and include (1) overlake convergence due to blocking by the Wasatch Mountains, (2) enhancement of blocking effects due to a horizontal moisture gradient, (3) flow deflection around the Oquirrh Mountains into an orographic concavity, and (4) hydrometeor transport into high terrain. These influences are not unique to the GSL region, and our results suggest applicability to other areas where lake-effect occurs in close proximity to mountain barriers, particularly in the case of small water bodies.