Why Michigan's summer in 2025 has been uniquely hot

Why Michigan's summer has been uniquely hot

While previous summers have had scorching temperatures, they have also had cooler weather move in at night. That hasn't been the case in 2025.

(FOX 2) - This year's summer has been one of the hottest - but maybe not for the reason people think.

The humidity has been a key part of why it has felt extremely warm. But to better measure 2025's summer, one has to dive into the data.

The backstory:

When people think of the hottest summers in Metro Detroit, they'll often cite 1988. There were five days that eclipsed 100 degrees and over 31 days that reached the 90-degree mark.

Accompanying those scorching temperatures was a drought that starved the region of water. It led to more fires around Southeast Michigan and a tough season for farmers.

But even with the extremes, the summer of 88 lands as only the 10th hottest summer in recorded history. That's because its average temperature was 74.2 degrees. 

By the numbers:

The best way to measure records over a time span as long as a single summer is by comparing the seasonal averages. That means using both the highs and lows of the days.

The hottest summer on record was in 2016 when the average temperature was 74.9 degrees.

Top 10 warmest Michigan summers

• 2016 – 74.9 degrees
• 2012 – 74.8 degrees
• 2005 – 74.8 degrees
• 1995 – 74.5 degrees
• 1955 – 74.5 degrees
• 2018 – 74.4 degrees
• 2011 – 74.4 degrees
• 2010 – 74. 4 degrees
• 2021 – 74.2 degrees
• 1988 – 74.2 degrees

Big picture view:

Because the summer of 2025 is not over, it's not included in the rankings. But as of Aug. 14, the average daily temperature is 74.3 degrees - making it one of the hottest. 

Here's the difference: this year's overnight lows have been some of the highest ever. The region has dealt with multi-day periods of sustained heat unlike any other year.

"When people talk about how hot it was back in 88, they're right to do so," FOX 2’s meteorologist Derek Kevra said. "But what they got was some relief days. We have had very few relief days this year."

In the summer of 1988, there were seven days when overnight lows fell into the 40s and 26 days with overnight lows in the 50s. The summer this year has had barely any nights when temperatures fell that low.

That included a 150-hour stretch where temperatures didn't even fall below 70 degrees. Over the entire month of July, only three days have fallen into the 50s. 

Local perspective:

Persistently hot stretches can present unique threats because of the lack of relief they provide. 

While it's the record-high temperatures that get the most news, studies have found more people die due to high temperatures at night. Research from The Lancet Planetary Health looking at 28 cities in Japan, South Korea, and China found a strong association between nights with excessive heat and mortality.

"The relative mortality risk on days with hot nights could be 50% higher than on days with non-hot nights," the study's findings found.

Adding to the risk is that nights are heating up faster than days, according to a 2018 climate assessment from the National Oceanic and Atmospheric Administration.

This means the window of time for somebody to cool their body down is shrinking. In the summer, for a city like Detroit whose residents lack air conditioning, this can have deadly impacts - especially on groups of people with health problems dealing with their heart and kidneys.