Endless Thread - Why it feels like it rains every weekend

Episode Date: July 11, 2025

If you feel like it's been raining a lot on the weekends this summer, you're not alone. A couple months ago, we noticed a thread on r/boston asking why? So, we enlisted the help of one of our WBUR colleagues, Climate and Environment Corespondent Barbara Moran to clear things up once and for all. Show notes: Rain Every Weekend??? (Reddit) OMG, why is it raining every Saturday in Boston? (WBUR)

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What's your official title? Correspondent? Are you a correspondent? Yeah. Of climate and environment, which fine. That's a fine title. But I always thought correspondence like went somewhere. Joining us from a cubicle 50 feet away. Exactly. Yeah. This is Barbara Moran. She is a colleague of ours here. WBUR where she corresponds on all things environment.

A few weeks ago, we gave Barb a mission. We needed her to get to the bottom of a mysterious meteorological phenomenon that people have been commenting on in the Boston subreddit. That phenomenon? Does it really? Does it really rain every freaking weekend? I had somebody tell me that they had been counting. It had been raining for 13 weeks on the weekend, somebody claimed to me.

Yeah, I think it was like 13 Saturdays in a row. Brutal. Horrible. And this Reddit thread threw out some theories about why this might be happening. Specifically, one paper that suggested it has something to do with the amount of pollution that we create over the course of the week. Barb went down the rabbit hole for us to find out if this is really a thing and it really does actually rain more on the weekends. and if so, why? Why?

Why? Why? I'm Ben's sunny boy Johnson. I'm Amory, don't rain on my parade, Severson, and you're listening to Endless Thread. Today's episode, raining on your parade. So I came into the story like you, where I think it was you or someone came to me and said, it's raining every Saturday. Is that like a thing?

And is there something about pollution? And I'm like, maybe, blah, blah, blah. So they said, look at this Reddit thread, which I did. And I'm like, okay, let's go. So I went down the rabbit hole, which is very interesting. I guess this is what you guys do over here, go down these rabbit holes. That's the whole point, right? We do be going down the rabbit hole.

We're a correspondent of the rabbit hole. Barb's first stop down the rabbit hole was this study we mentioned that was posted to the R-slash-Boston thread. Turns out this theory has a name. It's called the weekend effect. And this idea has been around for over a century. And here's the basic concept. Over the course of the week, pollution builds up, right, from cars and buildings and all this stuff. And all this pollution goes up in particulate matter and all these particles up into the sky.

And over the course of the week, until Friday, it's this big cloud of pollution that somehow seeds rain. And the rain falls on Saturday. wipes it out of the sky and then it starts over again on Monday. And so that's the idea. Can I ask you a question about that? Yeah, yeah, yeah. So the pollution that we're talking about in this theory. Theory description that you've just given us,

what is the pollution, quote unquote, that might be seeding the rain? That is such a good question. Yes. So the particular thing they're talking about is particulate matter, which are little teeny tiny particles or sometimes called aerosols, which are a product of the combustion of fossil fuels. So burning gasoline and oil, in addition to CO2, causes little particles. So in order to have rain, you need particles, right? They don't have to be little soot particles.

They can be any particles. You could have pollen. You could have dust. You could have this stuff from the fires, right? But each little particle is somewhere for water to condense. Okay. Okay. They're called cloud condensation nuclei.

That's what they call them, right? So. You should come up with a song about this, like an educational song. Yeah. Oh, I bet there's a condensation. Nuclear. Cloud condensation. Oh, I was imagining.

There's probably a magical bus. But I like, yeah. What's yours? I was more like cloud condensation nuclei. Ooh. Cloud condensation nuclei. Yeah. Okay.

All right, cool. Yeah. We've established. I love this. Okay, we got this. So you need these particles in order to have rain. That's a thing that I never think about is that like the water has to have a place to have a party so that there's a lot of water that will turn into a raindrop and that party spot is the nuclei. Oh my God. Absolutely. Boston's new hottest club is the cloud condensation nuclei. Okay. So in review, air pollution, like from cars. and fires and even dust and pollen, is made up of tiny particles.

These particles attract water molecules, which collect on each pollution particle until it's big enough to become a raindrop. And in theory, over the course of the week, when we are driving to work and polluting the planet, these particles build up in the atmosphere and thus cause rain. Yeah. It's a nice theory. Except it doesn't really have that much at effect. This has been studied a lot over time. And there is an effect. It does have a little bit of an effect. So the Reddit thread pointed me to an article and I interviewed an author. I am Maura Hahnberger and I'm an atmospheric scientist. And she found that there was this measurable effect. This is from a paper in 2008. Mostly, though, it came out on Wednesdays.

In most locations, the concentration of small particles is high. higher in the middle of the week. In some cities, it's Tuesday or Wednesday. Some cities, it's more like Thursday. But most locations, it peaks in there's more particles, more pollution in the air during the middle of the week. Sometimes it builds up if you have certain places like a valley. You get what's called an inversion and the air gets trapped. And then it can sort of build up and have a little more of an effect. But in most places, it's not a buildup that has any effect. Then I talked to this meteorologist named Matt Barlow up at UMass Lowell. I would say the jury is maybe still out as to whether perhaps in some locations it may have some modest effect.

That's not a scientist. That guy is definitely a scientist. There's no question that that does a scientist. I love that it. It was so much hedging in one sentence. Yeah. Okay. Interesting.

Can I add one point about this, which is very interesting, that everybody also told me that even any effect that it did have is much lesser than it was like 50 years ago, because we have a lot less of that type of pollution. Because cars and various things like burn much cleaner now. So there's a lot less of this particulate matter, the little particles. There is a lot less of that now than there was in the United States, 50s. years ago. So any, any effect that that would have caused is even less. Fewer nuclei parties to be had. All right. So pollution is probably not causing the rain. But it really does seem like it rains a lot on the weekends. I mean, it still feels very true.

And Barb doesn't give up that easily either. So she actually brought us another theory. And this one has to do with the jet stream and these weird patterns in it called, Rusty Waves. Do we need to go back and talk about the jet stream more? Should I tell you the theory first? I think maybe a quick definition of the jet stream and a song based on the jet stream would be warranted. Okay.

Here's what I learned. There's like a whole bunch of jet streams. Okay. Which is crazy. I thought there was one jet stream like that went around. Anyway, so a jet stream is like a fast moving ribbon of air that goes around the earth. Okay. Yep, yep, yep.

Okay. And we call it the jet stream because, you know, jets fly in it and they go faster one way or slower. Yeah. Yeah, yeah, yeah. The jet team isn't like a straight thing. Right. It goes, woo, you know, it's got all these big waves. You can't see Barb right now, but she's gesticulating in a very wavy way with her hands. Yeah.

She's ready for the cloud condensation nuclei club. Yeah, that's right. This professor at BU, Lucy Houtierre, said to me, she's, like, I'm not sure about this, but I've heard a theory that it can develop patterns in the jet stream that can sort of bring weather along like every seven to ten days. But these raspy waves don't care if it's Wednesday or if it's Sunday. It's just a periodicity in the cycle. But some years you could get unlucky and every Saturday it rains.

So Boston, interestingly, is very susceptible to undulations in the jet stream because we, sometimes it goes above us and sometimes it goes below us. And that causes a lot of weather effects around here. So in my brain, I had this image. If you can imagine a cartoon, like a cartoon gray cloud stuck in the jet stream. And it goes around the earth every seven days and lands on us and goes around. and goes around. And so that's what I'm thinking. Yeah, we drew the short straw of the global locations for the clouds travails.

Right. I like that idea because I'm like, oh, yeah, I get this. Yeah, yeah. Yeah, I'm like, okay, I get it. And then I'm like, no, that's not right. It sounds too orderly to me. Yeah. It is true that Boston has unduly influenced by the jet stream because it goes up and down right

around us and we get hit. And it is true that these sort of patterns can develop. And you can kind of get stuck in a chunk of the jet stream and that sort of bad weather can kind of loop by on sort of what seems like regular intervals. Okay. So the jet stream might have something to do with our rainy weekends. But is that it? Just wrong place, wrong time for those of us stuck in the stream?

Clouds are going to part and we're going to actually. get some clarity on this after a break. At Radio Lab, we love nothing more than nerding out about science, neuroscience, chemistry. But we do also like to get into other kinds of stories, stories about policing or politics, country music, hockey, sex, of bugs. Regardless of whether we're looking at science or not science, we bring a rigorous curiosity to get you the answers. And hopefully, make you see the world anew. Radio Lab, Adventures on the Edge of what we think we know. Wherever you get your podcast.

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Whatever your goal, we can help. Discover how the magic is made at WBUR.org slash creative studio. Okay, so here's where we are at. In order to have rain, you need clouds, which are tiny droplets or ice crystals floating up in the atmosphere. And you need something for that cloud condensation to, you know, party around. But cloud condensation nuclei aren't necessarily our weekday commute, pollute stuff. There is this other thing that could be messing with our heads when we're complaining about rainy weekends. The polar jet stream, which is this globe-encircling highway of air.

And yes, it definitely does bring wetter weather to the northeast, according to the meteorologists Barb spoke with. And if we're catching the rainy part of the jet stream on the weekend, and then seven to ten days later, it comes back around the next weekend. That could be part of the reason we keep getting rainy Saturdays. So they said, yes, this is sort of a thing, but that's not really what's happening. Okay. Dang it. So I said, well, what is happening? And they said, it's just really rainy and it's been raining a lot.

That's it? Yeah. That's the whole story? I'm sorry. There aren't two other little bits. Okay. To the story. Sure.

Okay. One is that climate change is making the variability worse. So we get more. bursts of heavier rain now. And it's just sort of like weirder, right? Like, it's like you get rain on its head of, but it like pours rain for like an hour. Yeah. And that clears up.

Yay, but too late, you're already soaked. Do you know what I mean? And so that is getting worse with climate change and is going to continue to get worse so the weather will continue to be more unpredictable, right? And yeah, this is kind of a bummer thing. but people wanted me to bring up, so I'm just bringing it up. The fact that we can have this conversation

is because we've collected all this weather data for 100 years. Oh, God. Right? You're going to tell me that in 2025, our president has decided it's no longer necessary to have this information. Yeah, and the information's already disappearing.

Really? Already weather predictions are getting less accurate. I hate this. Yeah. No, I hate this too. Okay, I have some follow-up questions. Yeah. When you say we're losing this data, is it being deleted, like the past data, or it's just that we're already losing the ability to collect more of this kind of information because positions are being eliminated, departments are being eliminated.

Both. So some data sets have been disappeared from the Internet. I mean, I'm sure they exist somewhere because people have been downloading stuff like mad, right? But there's also less weather data being collected. The weather stations in general are less staffed. There's talk of getting rid of whole systems of buoys that measure wind data on the ocean. Yeah, it's just all this stuff we take for granted is just going away. You know, you can joke about it.

You're not going to joke about it when you want to go on a little boat trip and then you run into a rock. Yeah. No, I don't think, I mean, all I can do is laugh to stop from crying. Yeah, I know. We should say that we recorded this conversation with Barb weeks before what we just witnessed last week in Texas. Devastating flash floods that killed more than 100 people with many still missing. There have been accusations from Texas officials, including the chief of the Texas Division of Emergency Management, that the National Weather Services forecast grossly underestimated the severity of the flooding.

But experts have told NPR and the New York Times that the forecast was as good as could be expected, especially given how quickly the storm escalated. There have also been questions related to Barb's points about loss of weather data and cuts to the National Oceanic and Atmospheric Administration and the National Weather Service. So did those cuts have anything to do with the National Weather Service? how well the agencies were able to do their jobs on July 4th, from forecasting to communicating. We have learned in the day since that one of the people who was not on the job last week was the longtime warning coordination meteorologist at the National Weather Service's Austin San Antonio

office. He took an early retirement offer this past spring after the Trump administration began cutting jobs at the National Weather Service. Another thing we know, data math, Relying on what is known and what has been studied and tracked is crucial for actually measuring how our climate is changing and the impacts of that change. Rather than relying on feelings and imperfect memories that reinforce the it's been raining all summer kind of narratives. One of the guys I talked to said that we have recency bias in that last fall it was really dry. It didn't rain at all. Nobody remembers that. Good point. Yeah, we were in drought for like a long time.

Yes. And it was like weirdly dry in the fall. Right. It was weirdly dry. I remember that now because I was like, November rain. Guns and Roses might have never written that song. You know what I mean? Come on.

Right. Well, I am aware that we're having this conversation in Boston, Massachusetts. Mm-hmm. And yet I imagine that other people probably feel this way are detecting patterns that either are or are not there about like, like the weekends in Lisbon or the weekends in insert other city. I would like to be in. That you would like to be in. Yeah, but it's like we're having a very Boston-centric conversation,

but I imagine this applies to people everywhere who are noticing like, oh yeah. In Boston, we say it's every Saturday in Tokyo. They're like, it's every Wednesday. Yes. Yes. Yes. This type of study has been done all over the globe and has found the same thing pretty much everywhere. It's like, oh, yeah, maybe you have this pattern and this pattern.

So, yes, people notice this type of thing everywhere except in Southern California, or it's always sunny. That's right. There's no point. You know what we need to do? We need to get rid of the work week. We need to stop working so that what we need to do. so that what we are viewing right now as it always rains on the weekends. It's like, no, no, it just rained on this day.

But the next day was sunny and clear. If we stopped thinking of it, we should just all stop working over the summer. Listen. I'm totally down with that. I would love that. As long as my pay keeps coming, I'm happy to stop working. Who do we talk to about this? That's your next investigative mission.

Barbara Moran, thank you so much for bringing us real answers and real data on this thing so that I don't go around telling everybody that it's raining on the weekends because of a Reddit thread. You have today stopped misinformation and I commend you and appreciate you for it. Thanks. Endless Thread is a production of WBUR, Boston's NPR. This episode was produced by Frannie Monaghan. It was hosted by myself, Ben Brock Johnson, and Amory Sebertson, with lots of help from Barbara Moran. Woot, Mix and sound design by Emily Jankowski. Our editor is Meg Kramer.

Our managing producer is Summit to Joshi. The rest of the team is Dean Russell, Grace Tatter, and production manager, Paul Weikas. You're doing like a sports announcer thing more than a meteorologist thing, right? Yeah, I know. I'm going to do the meteorologist thing and be like, Now, over here, if you have an untold mystery coming in from the West, or maybe a wild story that you never saw coming coming down from the North, please tell us about it.

Email us at endless thread at wbUR.org. Bye.