Seiche in Western Chippewa County, Michigan

Significant water level changes measured by water level equipment at the Point Iroquois, MI Light on the southern shore of Whitefish Bay as a mesolow at the heart of a decaying line of storms crossed the lake. A 3.75-ft change in water level from trough to peak during the morning hours is the largest in 30-years of water level records at Point Iroquois, MI. Water level fluctuations of 18 or more inches continued through the next day; elevated seiche activity was observed in the Whitefish Bay basin through the next several days.

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. Meanwhile, a strong mesolow developed at the heart of the slowly decaying thunderstorm complex, ultimately driving a meteotsunami across the length of Lake Superior, resulting in significant water level changes of as much as 2-4ft on Whitefish Bay and the Upper St. Mary's River during the morning hours. This resulted in delays in freighter traffic through the Soo Locks, the waterway through which nearly 100 percent of America's domestic iron ore passes. Periodic water level fluctuations up to 2 feet remained present on the eastern end of Lake Superior through the next couple days, and water levels did not settle back down to normal for several days through the end of June.