Lake Michigan’s Fall Turnover

Lake Michigan has held fairly steady in the 55F+ range. But we’ve noticed a recent downward trend in the water temperatures that most likely indicates the beginning of the fall turnover.

To give you a quick overview, during the summer the warmer air temperatures and longer periods of sunlight heat up the lake causing it to form three separate layers:

summerlake

Candidly, I don’t think we every really got a very deep epilimnion layer this summer. And with a colder thermocline lurking not too far below the surface, it’s easy to see how we had that goofy 55F cold spell in August that sent everyone shrieking out of the water.

But the fall turnover is something far more enduring. This takes place when the weather cools down during autumn and the sunlight diminishes on both ends of the day. As the surface temperature drops and the increased winds churn up the lake, the thermocline gradually deepens until the colder bottom layer starts to mix with the upper layers. This phenomenon is known as the fall turnover.

Lake_layers_fallturnover

Once the fall turnover takes place, we are at the “point of no return” as far as water temperatures are concerned. The lake will eventually form another surface layer during the winter months, but this will be much colder – and will eventually freeze over. The rest of the lake will be a uniform 39F until the spring winds, air temperatures, and sunshine mix up Lake Michigan for the spring turnover.

The key is, there’s no such thing as an “Indian Summer” when it comes to deep lakes like Lake Michigan. Once the fall turnover arrives, say goodbye to 50F+ water temperatures.

At least until spring…

4 Comments

  1. diver dave
    October 16, 2009

    ? WHAT ? THE WATER IS GOING TO GET COLDER AND ICE OVER THIS WINTER ? MR AL GORE HAS TOLD OF GLOBEL WARMING AND HOW WE WILL ALL DIE SOON ! I WAS HOPING TO WORK ON MY TAN AND SWIM ALL WINTER LONG. I JUST WISH I HAD NOT BOUGHT THAT CASE OF SUN TAN OIL LAST WEEK. MAYBE I WILL TAKE UP ICE SKATING ON THE LAKE. MAYBE WE CAN WORK ON A ROUTINE FOR THE ICE CAPADES !

  2. srhernan
    October 16, 2009

    You’re welcome! Actually, I would love to get a hold of one of the Chicago 2016 shirts. But between you and me, I wish they would have kept their original logo!

  3. southside Dave
    October 15, 2009

    All that thermocline talk this summer lead me to look it up on wikipedia. Your explanation was much better.
    ( your pic could of used a Chicago trade mark at the bottom of the lake, like say, a bunch of Chicago 2016 t-shirts ) Thanks for the write-up.


Mentions Of This Post

  1. […] I was going to be, given my narrowing window of opportunity. Lake Michigan had already begun its Fall turnover. Any day, a strong west wind could blow in and drop the lake into the 50′s – from which […]

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