How do the Great Lakes make nearby summers cooler and winters warmer?

The Great Lakes influence the regional climate by acting as a massive heat reservoir, which moderates the temperatures of the surrounding landmasses.123

This process occurs because water has a high capacity to store heat. During the warmer months, the lakes absorb large quantities of solar energy, which helps to cool the air passing over them, resulting in milder summers for nearby regions. Conversely, during the colder months, the lakes gradually release this stored heat into the atmosphere, which warms the air passing over the water and leads to less severe winter temperatures than would otherwise occur in the region.4123

This ameliorating effect is most pronounced on the downwind sides of the lakes. While this heat exchange moderates temperatures, it also influences local weather patterns, such as the formation of "snowbelts" along the eastern and southern shores, where winter heating of the air increases its instability and moisture content, leading to significantly higher snowfall in those specific areas.125