Marine Thunderstorm Wind · Lake Huron

Gust to 41mph at CMAN station APNM4, Alpena Harbor Light at 09:10. Gust to 46mph at KAPN, Alpena County Regional Airport, 6mi from the coast, at 08:55.

An unseasonably hot and humid air mass beneath a strong upper ridge in place across the Midwest led to the development of storms late on the evening of the 20th across the Northern Plains. These congealed into a thunderstorm complex over the Upper Midwest, tracking eastward along the perimeter of the ridge, into the Upper Great Lakes on the morning of the 21st. A NW-SE oriented broken line of storms developed along a warm advection axis ahead of the initial line of storms; this produced hail up to the size of golf balls across parts of northern Lower Michigan, including the Traverse City metro area, with a second round of storms crossing the area a few hours later. Meanwhile, a strong mesolow associated with the initial line of storms crossed Lake Superior during the morning hours and resulted in significant water level changes and attendant coastal impacts across the entirety of Lake Superior.