00:53 Dramatic Temperature Drop in 24 Hours for Lake Michigan Meteorologist Heather Tesch explains why parts of Lake Michigan experienced a 20 degree water temperature difference in just 24 hours.

At a Glance Parts of Lake Michigan's western shore have seen water temperatures fall from the 60s to the 40s this weekend.

Persistent winds pushed warmer surface water away from the shore. Water temperatures on the western shore of Lake Michigan have fallen dramatically over the weekend and persistent southwest winds are to blame.

A buoy near Winthrop Harbor, Illinois, or about halfway between Chicago and Milwaukee, reported a water temperature of 68 degrees Fahrenheit late Friday afternoon. Just 24 hours later on Saturday afternoon, the water temperature had plummeted to 48 degrees Fahrenheit.

There was a similar drop in water temperature at a buoy near Milwaukee which reported 62 degrees Fahrenheit Friday afternoon and then 43 degrees Fahrenheit on Saturday afternoon.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/southwest-winds-water-temp.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/southwest-winds-water-temp.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/southwest-winds-water-temp.jpg?v=ap&w=980&h=551 800w" > Analysis of water temperatures on the southern end of Lake Michigan as of Sunday. The yellow, green and blue shadings from near Chicago to north of Milwaukee represent cooler waters in comparison to the rest of the lake. (NOAA Great Lakes Environmental Research Laboratory)

Strong southwest winds caused this rapid but localized drop in water temperature by pushing warmer surface water away from the shore of Wisconsin and northern Illinois. When that happens, colder water from deeper in the lake rises to the surface.

You can see this in the water temperature analysis above from Sunday which has cooler water right along the shore and warmer water to the east and south across Lake Michigan. For comparison, the water temperature on the southern part of Lake Michigan was in the 70s on Sunday morning.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/graph-water-temp.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/graph-water-temp.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/graph-water-temp.jpg?v=ap&w=980&h=551 800w" > The blue graph line in between the two red arrows shows the massive water temperature drop in 24 hours near Winthrop Harbor, Illinois. (NOAA)

This phenomenon, which is called upwelling, also occurred on the eastern portion of Lake Michigan's shore last week.

A buoy near South Haven, Michigan, registered a water temperature drop from 75 degrees Fahrenheit last Monday to 49 degrees Fahrenheit 24 hours later. In that case, strong northerly winds were the culprit for the upwelling. The water temperature at that buoy has since risen back into the middle 60s .