Water temperatures in the 70s one day and then in the 50s the next! Upwelling might help explain why this happens. 

What You Need To Know

  • Dramatic changes in water temperature are common on Lake Michigan
  • Wind direction is key to determining how warm or cold the lake will be
  • Upwelling is the process in which cold water from below pushes to the surface

If you've ventured to the lakeshore much this summer, you might have noticed the dramatic water temperature changes from day to day. One day the water might be a comfy 75 degrees and then the very next day an icy 58!

In order to understand why this happens lets first look at the water temperature through the entire depth of the lake.

In this graphic courtesy of NOAA, we are looking at the surface water temperatures and notice most of them are in the 60s and 70s (yellow and orange colors). 

On calm days in the summer without much wind, this warmer water remains on the surface and we get to enjoy jumping in the lake. 

In this next graphic, we are looking at the water temperatures at the bottom of the lake and notice the huge difference. Even this time of year, they can be very chilly in the 40s and 50s!

On days with strong winds, especially an offshore wind, this cold water is able to mix and be brought to the surface of the lake. This process is known as upwelling.

This graphic, also courtesy of NOAA, might help explain things better. 

Notice when we have a strong offshore wind, the top layer of warm water is pushed farther out into the lake. Colder water from below rushes up to the surface to replace the water that has been displaced. This helps explain why we can see such large temperature extremes from day to day.

It all has to do with the wind!