A line of severe thunderstorms pushed across Lake Michigan Monday evening. The wind blowing during the severe thunderstorms turned Lake Michigan into a sloshing bathtub.
The line of severe thunderstorms was a derecho, which is a long-lasting line of very severe thunderstorms. A derecho is characterized by a long path of significant wind damage. Monday’s derecho caused severe damage from South Dakota through Iowa, Wisconsin and Illinois. Fortunately the derecho weakened rapidly as it moved into western Lower Michigan.
But the strong winds definitely sent Lake Michigan’s water levels into a tizzy. The National Weather Service reported Lake Michigan’s water level rose one-and-a-half feet at South Haven as the storm line approached Monday evening.
Look at the water level graphs at Holland, MI and Milwaukee, WI. The graphs start on August 8 and continue to August 14.
Water levels at Holland, MI from August 8 to August 14, 2020. (Data from NOAA)
You can clearly see when the line of storms hit Holland last Monday evening. At Holland, Lake Michigan initially rose about one-half foot and then plunged about one foot. Then over the next four days the lake level has very rhythmically risen and fallen. Gradually over the last four days the rise and fall has become smaller.
The same situation is occurring on Lake Michigan at Milwaukee, WI.
Water levels at Milwaukee, WI from August 8 to August 14, 2020. (Data from NOAA)
At Milwaukee there were at least two rise/fall patterns that measured around one-and-a-half-feet. Again, after the intial big rise and fall, we see a very regular pattern of diminishing rises and falls.
It seems as though a wave is still sloshing back and forth on Lake Michigan. The wave hits one shoreline and then bounces back to the other shore.
Other parts of Lake Michigan aren’t showing that same sloshing back and forth.
Water levels at Calumet Harbor, IL from August 8 to August 14, 2020. (Data from NOAA)
The graph above from Calumet Harbor shows when the storm hit, but doesn’t have the same symmetrical wave pattern after the storm.
Water levels at Ludington, MI from August 8 to August 14, 2020. (Data from NOAA)
Farther north on Lake Michigan, Ludington’s water levels also show no super rhythmical wave pattern.
The shorelines are shaped and angled differently at Calumet Harbor and Ludington, which is probably the reason for the different look on the water level graph.