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Climatologist: Minnesota's most humid days are becoming more humid

Kenny Blumenfeld, a DNR senior climatologist, said Minnesota's most humid days are becoming more humid — making some of our heat waves more extreme.

ST PAUL, Minnesota — It's not the heat, it's the humidity. 

"I know it's a cliché but it's true because that's really what you feel," said Kenny Blumenfeld, a senior climatologist with the Minnesota Department of Natural Resources. 

Minnesota's most humid days are becoming more humid and making some of our heat waves more extreme. 

According to Blumenfeld, extreme-humidity heat waves have also become more common in Minnesota. 

"It's not that every time we get hot it's more humid than it used to be or that it's always more humid than it used to be. What it is, is that occasionally we get these very extreme events that are still pretty rare but they are delivering a level of humidity that we just never used to have and those are the days that are likely to become more common as we move into the future," Blumenfeld explained. 

While it's hot outside, it's been a while since Minnesotans have experienced an extremely humid heat wave. The last one was July 19, 2019 when the high in the Twin Cities was 95, with a dew point of 80. 

Monday's temperatures did not rise to that level. At MSP Airport, the dew point reached 68. When talking about really humid heat events, Blumenfeld said they're referring to ones where the dew point remains at 70 or higher throughout the day which has not happened so far this year. 

Extreme heat waves are now more likely to be caused by humidity than before. It can become dangerous and harder for the body to cool down. 

"What we see overall is a slight increase in the frequency of the really extreme heat events but they are dominated by humidity. So you wouldn't recognize them from their temperatures alone. It looks like a normal hot day... it's 95 or 97 degrees. The difference is — with increasing frequency — those days have dew points of 75, or 77, or even 80 degrees and that's when you start getting into unbearable conditions that used to be unheard of in Minnesota and are now slightly more common," Blumenfeld said. 

So why is this happening? With climate change, rising global temperatures have led to more water coming off the oceans and getting into the air. 

"That's the air that then gets pumped up here whenever we get a big, hot, humid air mass in. So there is some indication that as global temperatures rise, you're getting more humidity in some of the most extreme air masses because there's just more water around in the air," Blumenfeld said.

Another factor could be there's more agriculture in growing regions which also ends up putting more water into the atmosphere. 

"There's some evidence that some of our most extreme days have at least been influenced by that kind of humidity but we're also seeing these conditions of occasional extreme humidity-driven heat waves in areas that don't have a lot of agriculture," Blumenfeld said. 

There are challenges with trying to quantify the changes in our humidity as these extreme-humidity heat waves are rare and do not occur every year. 

Blumenfeld added, "This stuff is supposed to be complicated. It's science. It's never going to be this straight-forward message that people want." 

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