Influences of Orography and Coastal Geometry on Lake- and Sea-Effect Storms Formed over Lake Ontario and the Sea of Japan

The interactions of lake- and sea-effect precipitation systems with surrounding shorelines and orography often complicate the accurate prediction of these snowstorms, which can produce large and very localized snowfall accumulations. This presentation will examine the factors influencing precipitation distribution and magnitude during two such events. The first impacted the modest Tug Hill Plateau, which lies east of Lake Ontario in eastern North America and observes some of the most intense snowstorms in the world. In situ observations and WRF simulations of this event show that orographic precipitation enhancement was not the only contributor to the Tug Hill precipitation maximum: the large-scale flow, Lake Ontario’s asymmetrical shoreline geometry, and differential surface heating and roughness contributed to the development of three major airmass boundaries, which shaped the distribution of precipitation inland. The second event occurred in the Ishikari Bay region of western Hokkaido Island, Japan, where sea-effect precipitation generated by the Sea of Japan produces prolific cool-season snowfall accumulations. During this transverse-mode sea-effect storm, thermal and roughness gradients along the downstream coast’s curving shoreline, together with orographic flow deflection by the coastal mountains, contributed to convergence and ascent along an elongated, quasi-stationary region of precipitation enhancement that extended inland from the coast. Similar synergistic contributions of orography and coastal geometry are likely found in other lake- and sea-effect regions, with implications for numerical weather prediction and operational forecasting.