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Cooler fall air can be a breeding ground for viruses — local meteorologist Tawana Andrew explains

A view of downtown Louisville that includes the river, buildings and cars.
Gabrielle Jones

Lower humidity feels great, but can be a problem, too. Learn more in the latest edition of "Science Behind the Forecast."

Did you know bacteria can move around more easily when air humidity is 40% or less?

Every week WAVE 3 meteorologist Tawana Andrew breaks down what we know and what we don't about the climate and weather here in Louisville. Check out our most recent conversation about why humid summer air, though uncomfortable, isn't always a bad thing.

Bill Burton: It's time for us to take a look at the "Science Behind the Forecast" as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning, Tawana.

Tawana Andrew: Good morning, we're getting closer to the official start of fall, which means lower humidity coming into the forecast a little bit more.

Bill: I'm already enjoying the lower temperatures and the lower humidity. But unfortunately, there's a bad side or can be a bad side to lower humidity. That's our topic today. What do we need to know about lower humidity?

Tawana: Well, first, it's important to remember that cold air overall holds less moisture than warm air. So that's why as our temperatures drop, our humidity also goes down. And when the humidity is low, existing water is quickly and easily pulled into the air and it has to come from somewhere. So moisture evaporates more rapidly from our bodies in these types of conditions. And that could lead to several potential health risks in this really nice weather.

Tawana: So first off, lower humidity air is an excellent breeding ground for viruses and bacteria. When you have the humidity dropping below 40%, dangerous microbe containing aerosols can easily move around round a little bit more freely. And that means they can infect us and make us sick a little bit more easily at especially at a higher rate as well, once that humidity starts to go down. And keep in mind this is why while it's stuffy on those summer days, we're not as stuffy, you know, we're not as feeling as sick.

Bill: I see what you did there. Well played. Very, very good.

Tawana: Thank you. But yeah, water vapor actually helps to limit the spread of these microbes. So that's why in the summer months, that high humidity is actually helping us out. Now I mentioned of course that the moisture on these lower humid humidity days has to come from somewhere. And sometimes that moisture in our nasal passages in our bronchial tubes will evaporate more easily in these types of conditions that also can make our airways more easily irritated and make us more susceptible to viruses and bacteria. Viruses also survive longer in lower humidity. So that's another reason why more of us tend to get sick during the colder and drier months. So it's not just the fact that you know, we're all crowding inside to stay warmer, is that viruses are basically having a party and thriving while the weather is a little bit dry. So and it's and it's not just those mold, mildew mites, other allergens tend to thrive in dry air, so anybody with asthma tends to know that when it gets drier, their symptoms sometimes can intensify. So that's why you got to make sure humidifier things along those lines, you have one of those to make sure you are staying as safe and as healthy as possible. And we all sometimes get a little itchy notice our skin is a little bit drier as well in these lower humidity days because literally the air is sucking the moisture from you like a vampire that way.

Tawana: So it's taking the air out of our skin or hair cuticles when the humidity is low. So while it feels absolutely fabulous outside for the moment, it's important to remember that the moisture that we have in the air sometimes is not always a bad thing.

Bill: True. But now we have a better understanding why low humidity feels good. But there could be danger lurking and we know this thanks to the latest edition of "Science Behind the Forecast" with WAVE 3 meteorologist Tawana Andrew. Thanks for the knowledge, Tawana.

Tawana: Of course.

Transcript has been lightly edited for clarity.

Bill Burton is the Morning Edition host for LPM. Email Bill at bburton@lpm.org.