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Ready for a swim? Lake Michigan is heating up!

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Posted at 1:01 PM, Jul 09, 2020
and last updated 2020-07-09 14:01:23-04

Lake Michigan is heating up!

Surface temperatures on the lake are largely in the 70s, low to mid-70s on the west side of the lake, with upper 70s to low 80s on the east side.

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Lake Michigan surface temperatures as of July 8

So how do these temperatures compare to normal? Well above average!

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This graph shows that Lake Michigan surface temperatures are running well above normal

The graph compares the current average Lake Michigan surface temperature to the long term average (1992-2019). It's easy to see the red line, representing 2020 surface temperatures, has climbed quickly in the last few weeks. The average surface temperature of the lake is not just above the July normal, but has now exceeded the average warmest temperatures normally experienced on the lake. The average surface temperature normally peaks in August at around 70-degrees, and we are already well above that.

However, this is not the first time we have seen Lake Michigan temperatures climb above average. We don't have to look too far back in time to find another above average year.

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2018 Lake Michigan temperatures compared to average

In 2018, Lake Michigan temperatures similarly climbed above average in late June and early July, and stayed above normal through most of the summer.

So what is the reason for the big jump in Lake Michigan surface temperatures? It's no surprise that temperatures over the last few weeks have been largely above average for us in Southeast Wisconsin. But it's not just here, temperatures for our Lake M neighbors in parts of Illinois, Indiana, and Michigan have been running above normal as well, contributing to the warm-up.

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But it's not just the warm temperatures, it's a combination of the heat AND the lack of wind. The weather set up over the last few weeks has featured relatively weak winds. Without the wind to help stir up the lake, creating waves and upwelling, surface water temperatures have surged.

Notice, the subsurface water temperatures are still cool, in the 40s and 50s.

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At the bottom of Lake Michigan, temperature readings are still in the 40s

Better mixing of the bottom water and the surface water would help to cool temperatures back down. Until we get some significant wind, lake temperatures will continue to run above normal.

If you have a question for the TMJ4 Storm Team, or an idea for a blog, let us know, weatherteam@tmj4.com.

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