Lake Michigan can make some crazy temperature changes. Saturday, the temp. at the Chicago Water Intake (Harrison-Dever Crib) reached at least 94.1°. The intake is 2.75 miles east of downtown, the Lake Michigan surface water temp. was 69°. It’s very unusual to get a temp. that warm. Midway Airport got to 97°. There was a brisk southwest wind, so the air wasn’t spending a lot of time crossing those 2.75 miles.
At 4 pm, the air temperature was 92.3°, the relative humidity was 49% and the wind was southwest at 15 mph with a peak gust of 38 mph. One hour later, at 5 pm, the temperature was 72.6°, the relative humidity was 95% and the wind was northeast at 22 mph with a peak gust of 32 mph.
That’s a one-hour temp. drop of nearly 20 degrees, the relative humidity goes up 46% and look at the air convergence going on where that southwest wind met the northeast wind.
Same story at Michigan City, Indiana (pic. with rainbow in upper right from Sat. at 7:33 pm). In one hour the temp. dropped from 91.2° to 75.6° and the wind went from SW at 18 mph to NE at 27 mph.
And at Milwaukee WI, the temp. at 1pm was 87.3° – at 2 pm it was 64.0°. The wind shifted from due SW to NNE and gusted to 35 mph. Air can’t go down into the water, so all that air was coming together and lifting up, helping to build up the storms. Speaking of storms:
This was the S. Haven buoy camera Sat. evening showing a thunderstorm and shelf cloud approaching from the northwest. The buoy had a high temp. Sat. of 79° and a low temp. of 73°. The peak wind gust with the storm was 36 mph. Waves increased to 3 feet. Remember, cold air coming over warm water makes bigger waves than warm air coming over cold water.
The water temp. at the S. Haven buoy was 76.1° Sat. evening. At a depth of 36 feet, the water temp. was still 74.6°. But…at a depth of 43 feet, the water temp. was 54.4° and at 56 ft., the water temp. was only 46.0°. If we were to get a day with a brisk northeast or east wind (uncommon at this time of year), the warm surface water could be blown back toward the middle of the lake and the colder water below could rise to the surface. That process is called “upwelling“.
BTW, the South Haven and Port Sheldon buoys are self-funded projects. There is a GoFundMe page set up for anyone who would like to help keep the buoys out there next summer.
This is South Haven Saturday PM 7/20/19. The boats are racing to get back into the channel. There is a rapidly approaching thunderstorm in the distance to the northwest with a nice approaching (and windy) shelf cloud. The peak wind gust with this storm was 53 mph and the wind shifted 170 degrees from 190 deg. (almost due south) to 000 deg. (due north).