Sensitivity of Lake-Effect Snowfall to Lake Ice Cover and Temperature in the Great Lakes Region

In recent years, climate models have used relatively coarse resolution grids to determine trends in the Earth's environment on the time scale of months, seasons, and years. Increasingly, efforts are being made to explore how these long term changes impact hourly and daily weather systems. Due to the relatively coarse horizontal resolution of climate models, they cannot resolve the small scale features associated with daily weather patterns, which can be affected by evolving climate conditions. One region in which changing large scale climate conditions may significantly influence local-scale feedbacks is the Laurentian Great Lakes. The cold season is of particular interest, as climate conditions can impact lake surface temperature, ice formation and intensity, along with snow distribution and intensity. The results presented in this study are important for preparing infrastructure to handle potentially extreme weather conditions in a future climate.

In this study, high-resolution WRF model simulations are used to explore the sensitivity of the Great Lakes' lake-effect snowfall (LES) to changes in lake ice and temperature. A control simulation with typical ice cover is compared with three sensitivity tests: complete ice cover, no lake ice, and warmer lake surface temperature. Complete ice cover is found to eliminate lake effect snowfall, while LES placement in cases with at least a partially unfrozen lake surface is determined by the location of lake ice. Removal of ice cover results in expansion of the area affected by LES, while an increase in lake temperature primarily increases snowfall amount. There is no change in LES morphology for differing lake surface properties. With increases in lake temperature and removal of lake ice, water vapor content increases in the boundary layer. The increased water vapor source leads to higher snowfall intensities, while the topographic features over land strongly affect the placement of the snow bands. The results imply that realistic simulations of the position and occurrence of lake ice cover are essential for long term simulations of winter precipitation and climate over the Great Lakes and warmer lakes with reduced ice can increase the spatial extent and magnitude of LES.