Colder by the Lake in the Winter
On strong radiational cooling nights, such as clear skies and light winds, dense cold air at the surface drains from the higher elevations down to the low elevations near Lake Superior. When the lake is unfrozen, it usually keeps temperatures warmer during the fall, winter, and into early spring. When the head of the lake freezes, cold air does not modify so easily, especially if the ice is snow covered. The air can then become colder than the surrounding higher terrain. One little quirk with the drainage process is that air warms when it sinks in elevation. The warming will be at least partially balanced off by the radiational cooling that occurs at the same time.