Influences of Coastal Geometry and Orography on Lake- and Sea-Effect Precipitation

Cold-air intrusions over bodies of water such as the Laurentian Great Lakes and the Sea of Japan frequently produce intense snowfalls and prolific seasonal snowfalls, especially over downstream topography. The Tug Hill Plateau, which rises 500 m above the eastern shore of Lake Ontario, observes a mean annual snowfall of over 700 cm on its western slope and experiences some of the most intense snowstorms in the world. In the mountains of northwest Japan, snowfall generated by the Sea of Japan during the Asian Winter Monsoon contributes to an immense snowpack that can exceed 6 meters in depth. Sukayu Onsen in the mountains of northern Honshu may be the snowiest observing site in the world with a mean annual snowfall of 1764 cm and a mean January snowfall of 459 cm.

Drawing on observations from the Ontario Winter Lake-effect Systems (OWLeS) field program, the A-train satellite constellation, and Japanese radar and snow networks, and well as real-data and idealized numerical simulations, this presentation summarizes recent advances in our understanding of the influences of coastal geometry and orography on lake- and sea-effect precipitation. The coastal geometry of Lake Ontario and Japan's Hokkaido Island strongly influences the forcing of long-lake-axis parallel and transverse-mode snowbands, respectively, affecting the distribution and intensity of snowfall downstream. Land-breeze fronts generated by Lake Ontario can extend downstream and inland, affecting snowfall rates over the Tug Hill Plateau. The inland penetration and orographic enhancement of lake- or sea-effect precipitation in both regions increases with the intensity of the incident flow, but radar echo characteristics (e.g., tops, reflectivity variability, etc.) over downstream topographic features differ between the two regions. These findings contribute broadly to our understanding of lake- and orographic precipitation processes, with implications for operational forecasting and climate applications.