Steven says thunder fever is a rare condition, and has never been documented in this part of the country. It's caused when high humidity from thunderstorms leads to pollen swelling up and breaking into tiny particles.
Those smaller particles can then get into a person's lungs much easier and lead to health problems.
"Particularly in somebody who's highly allergic to those pollens, now you’re getting a much greater allergen load deep in the small airways of the lungs," said Steven. "They have a much worse allergic reaction deeper in the lungs than people have ever had before."
"I was wondering what was going on cause usually I don’t have this big of an issue but today was special," said Melanie Mitten, from Wauwatosa.
Steven says our late spring temperatures have caused all of the trees to pollinate at the same time, instead of staggered like in a typical allergy season.
That means the season will be much shorter, but more severe.
While Steven says the Midwest has never had a documented case of thunder fever, an outbreak in Australia two years ago led to 8,500 hospitalizations and nine deaths from severe asthma attacks.
"I’m not sounding any alarms or anything but I think it would be prudent for people, particularly those who know they are highly allergic to tree pollen, if they don’t need to be outside during or shortly after the thunderstorms, probably not be a bad idea," said Steven.