November Witch

During autumn, two major weather tracks converge over Lake Michigan. Cold, dry air moves south/southeast from the province of Alberta and northern Canada; warm, moist air moves north/northeast from the Gulf of Mexico, along the lee of the central Rocky Mountains. The collision of these masses forms large storm systems in the middle of North America including the Great Lakes. When the cold air from these storms moves over the lakes, it is warmed by the waters below and picks up a spin.

The result is referred to as a "November gale" or "November witch". Fuelled by the warm lake water, these powerful storms may remain over the Great Lakes for days. Intense winds can ravage the lakes and surrounding shores, severely eroding the shoreline.