Mechanisms of Lake-effect Forcing and the Tug Hill Precipitation Maximum during OWLeS IOP2b

Lake-effect storms frequently produce a precipitation maximum over the modest Tug Hill Plateau (hereafter Tug Hill), which rises 500 m above the eastern shore of Lake Ontario, and experiences some of the most intense snowstorms in the world. Improved understanding of lake-effect formation, maintenance, and precipitation enhancement mechanisms is crucial for weather forecasting around Lake Ontario and other lake-effect regions. Building upon prior observational research, here we use Weather Research and Forecasting (WRF) simulations to examine the mechanisms responsible for the Tug Hill precipitation maximum observed during IOP2b (December 11–12, 2013) of the National Science Foundation sponsored Ontario Winter Lake-effect Storms (OWLeS) field campaign. Our simulations show that the large-scale flow, Lake Ontario’s shoreline geometry, and differential surface heating and roughness contributed to the development of three major airmass boundaries, a finding that is supported by observations collected during OWLeS. The first was a land-breeze front that formed along a bulge in the south shoreline and extended downstream over eastern Lake Ontario, playing a primary role in band development. A key contributor to inland precipitation enhancement over Tug Hill was a second land-breeze front, which formed along the southeast shoreline and extended inland and northeastward across Tug Hill, cutting obliquely across the lake-effect system. Localized ascent along this boundary contributed to an inland precipitation maximum even in simulations in which Tug Hill was removed. Ascent over Tug Hill did, however, intensify and broaden the ascent region, increasing parameterized depositional and accretional hydrometeor growth and reducing sublimational losses over Tug Hill. These results highlight the multi-faceted nature of lake-effect system development and inland evolution, especially the contributions of shoreline geometry and mesoscale airmass boundaries. These land-breeze fronts appear to be unidentified previously and may be important in other lake-effect storms over Tug Hill.