Seiche on Lake MichiganJuly 11th, 2011 at 10:56 pm by Bill Steffen under Bill's Blog, Weather
Click the image to enlarge. On July 4, 2003, seven people lost their lives at the Lake Michigan shore near St. Joseph. A line of storms with strong winds crossed the southern part of Lake Michigan. The storms caused a seiche (pronounced “saysh” with a long “a”). A seiche occurs when the strong winds of the storms push the water from one side of a Great Lake to the other. In this case (July 11, 2011) we had a strong west wind that pushed the water toward the Michigan shore. The water “piles up” at the Michigan shore and the water level gets higher. In Wisconsin and Illinois, the water level dropped. As the storms push inland into Lower Michigan and the wind dies down at the lakeshore, the water starts to move back toward Illinois and Wisconsin. The water can slosh back and forth for hours. The retreating water creates strong rip currents that can carry swimmers away from shore into deep water. This is a graph of the water level today (7/11/11 on the right part of the graph) at Calumet Harbor in Chicago. It looks to me that the water level fell 8″ then rose about 28″. Cort can correct me if that’s not right. UPDATE: Cort sent me this article about the water retreating at Tunnel Park. Think of the power needed to push that much water around. A cubic foot of water weights 62.4 pounds. Check out the full graphs here. Note that as the storm hit there was an almost instantaneous spike of rapidly rising air pressure, a smaller upward spike in humidity and a downward spike in temperature. Remember, on those rare occasions when we get a line of storms with strong winds, you’ll want to avoid going back into Lake Michigan until we know that there either is not a seiche, or that a seiche that is occurring has ended and the lake has calmed down. By the way, look at the SPC storm reports from Monday and you’ll see that the derecho thunderstorm outbreak went from NE Illinois and SW Michigan all the way to Maryland.