Authors

Abstract

The surface of the Great Lakes interacts with the atmosphere, influencing the weather and climate over the Great Lakes Region (GLR). However, most climate models were not designed with sufficient emphasis on lakeatmosphere interactions, which could potentially cause model biases over the GLR. To understandhow lake surface temperature (LST) affects the regional summer climate over the GLR, we conducted twin experiments using the Weather Research and Forecasting model at a spatial resolution of 4 km using two different LST data sets as the bottom boundary condition over the Great Lakes. Our simulations include 10 ensemble members for the summer of 2018 and a single multiyear run for the summers of 20142020. Results show that variations in LST influence atmospheric temperature and moisture at a local scalewhile affecting the convective environment and precipitation processes over a much larger spatial scale. In particular, an LST that is only 1C3C warmer (depending on the lake) increases near-surface air temperature by 1.93C and 0.97C over Lake Superior and Lake Erie, respectively, and increases evaporation over the lakes by 0.23 and1.1 mm day1. The warmer LST reduces mesoscale convective precipitation upstream of the GLR; however,it increases isolated deep convective precipitation and nonconvective precipitation downstream of GLR dueto increased local instability and enhancement of moisture transport. Our analyses confirm the robustness of these impacts, which is at least 2 times larger than the model internal variability and is seen across all simulated summer seasons.