Heat wave makes Lake Michigan.. colder?

Where I work, we look at water temps in Lake Michigan (Chicago area) daily. Here’s some temps from the previous week:

7/28
CHICAGO SHORE…77
CHICAGO CRIB…69

7/29
CHICAGO SHORE…79
CHICAGO CRIB…68

7/30
CHICAGO SHORE…79
CHICAGO CRIB…69

7/31
CHICAGO SHORE…77
CHICAGO CRIB…66

8/1
CHICAGO SHORE…76
CHICAGO CRIB…63

8/2
CHICAGO SHORE…58
CHICAGO CRIB…56

8/3
CHICAGO SHORE…62
CHICAGO CRIB…53

This coincides with a heat wave that has affected the region. So, what’s going on here? I’m guessing one of two things:

  1. The temps aren’t accurate;

  2. Something’s happening where warm water is descending or moving elsewhere horizontally, and colder water is rising/moving is from elsewhere.

Anyone know?

oh, and the links to the data FWIW: SXUS83 KLOT - Google Search

Couldn’t it be something as simple as evaporative cooling?

I believe the term is “current” as in the Gulf Stream current which is responisble for the even warm weather on the Burmuda island and the warmer than expected weather in Great Britan.

That seems to be pretty much it:

From a Chicago Tribune article (which may require registration).

Barrytown - thanks! That does explain it. I see I wasn’t alone in doubting the readings; looks like I was in good company:

Good find!