It's been a windy and wavy month along the shores of Lake Michigan. In fact, near record summer wave heights were observed from July 27-28th as persistent strong northerly winds resulted in waves over 10 feet! Additionally, water temperatures were 10 - 15 degrees below normal during this time, dipping into the upper 50s in parts of the lake. Lets examine the causes of the record cold water and high wave heights, along with the connection between the two.
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Using the Southern Lake Michigan Mid-Lake Bouy as our reference (as seen in the image @ 8.5 ft), waves of 8+ feet are common during the winter months, however quite rare in the summer. Wind is the driving factor in producing waves in the Great Lakes, and are maximized with a strong wind blowing along the longest part of the Lake. So, in Lake Michigan, waves are maximized with a north to south wind. While the summer is generally correlated with lighter winds, persistent northerly winds up to 40 mph on July 28th resulted in wave heights of 8.5 feet at the bouy, which was the 3rd highest July reading since 1981! Waves were as high as 12.4 feet along the Indiana coast, which was recorded at the bouy just off the shore of Michigan City.
The strong winds had additional effects besides a breezy day with high surf. The combination of wind and waves also acted to cool the lake significantly by a process called upwelling. Upwelling is when the cooler water, deeper in the lake becomes mixed with the water at the surface. The result this July was temperatures in the upper 50s, when they are usually in the upper 60s and even 70s! The reading of 58.8 degrees at the Southern Lake Michigan Bouy on July 28th was the second latest date of all-time the water was that cold during the summer months!
