Observational Analysis and Numerical Simulations of a Case of Rotating Lake-Effect Snow over Lake Tahoe

A distinctive lake-effect snow event occurred over Lake Tahoe on 27 October 2004. The event featured a series of convective cells well observed by the Reno, NV WSR-88D radar (KRGX) that developed over the lake. Three of the five individual cells that developed during an approximate 13-hour period contained cyclonic rotation. In order to better understand the causal mechanisms behind the pulsing and rotating behavior of the lake-effect convection, a detailed observational analysis was conducted and supplemented with simulations using the Weather Research and Forecasting (WRF) numerical model. Observations and WRF simulations show the development of a land breeze, particularly along the eastern lake shoreline, that lead to an enhanced low-level, over-lake convergence zone. WRF simulations suggest that the pulsing of the lake-effect convection may have been due to cyclical buildup and release of instability over the lake. This event is an excellent example of a lake-effect snow event developing over a small lake surrounded by complex terrain and provides insight into the fundamental mesoscale processes linking the evolution of lake-effect convection to over-lake instability.