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Are weather apps lying? The truth is in the dew point.

Not all 75°F days are created equal.

A dark-haired man in a light purple shirt and light blue pants walks away from the camera on a city street, in bright sunlight. His shirt has a soaked patch where sweat is spreading across his back.
This man is sweaty. I empathize with his pain.
Michael Nagle/Xinhua via Getty Images
Alex Abad-Santos is a senior correspondent who explains what society obsesses over, from Marvel and movies to fitness and skin care. He came to Vox in 2014. Prior to that, he worked at the Atlantic.

Editor’s note: Summer 2023 has been one of the hottest on record — although one of the coolest we’ll ever see again — and we could all use a little help navigating the heat. Below is an interview from 2022 (another hot year!) that seeks to help you read your weather app.

When a 72-degree day feels like a swampy armpit, I start to realize that everything I’ve ever thought I understood about weather, mainly temperature, is a lie. Sweating through my shirt, wiping my brow, and staring in disbelief at my weather app wondering, “How could this be the 72°F I know and love?”

Thankfully, I’ve found a better number to tell me how it’s going to feel outside — and it’s not the relative humidity, which is also a sham. It’s the dew point.

The lower it is — ideally in the 50s to 60s — the less sticky it will feel. The higher it is (70s) the closer it will be to my personal hell. (The relative humidity, a sometimes popular metric, measures the dew point against the temperature, making it particularly unhelpful on very, very hot days, when the temperature may be much higher than a relatively low, but still uncomfortable, dew point.)

In an effort to better explain why the dew point is the superior way to tell the weather and what it exactly means, I spoke with John Homenuk on a recent rainy, uncomfortably sweaty afternoon. Homenuk, who studied meteorology at Kean University, is a dew point enthusiast and the reason I found out about dew point forecasts in the first place. He’s the force behind the New York Metro Weather Twitter account.

New York Metro Weather has a 58,000-plus following that looks to it to answer a really simple question: Is the weather in New York City today going to be good or bad? Homenuk gives his followers a vibe rating out of 10 (sunny, humidity-free days score the highest) and sprinkles in a brief explanation of why it will or won’t be a pleasant day in New York.

As Homenuk confirmed to me, not all 72°F days are created equal — and the dew point might be the best explanation why.

It’s a pleasure to speak with you. In your words, the vibes in New York are awful today.

Yeah. We kind of need it though. We’ve been in such a bad drought. Sometimes I have to try really hard to keep what we need in terms of weather away from what the actual vibe is — today is definitely two out of five.

I think what makes it stink is that it’s very sticky outside. It feels like I’m in a low-temperature sauna.

Right! Like a cooler rainy day is pretty nice.

Yeah, and I wanted to ask you about what makes it feel cooler.

I’m recently — in large part because of your Twitter feed — a dew point convert. The dew point is high today and it feels disgusting. And I know that the weather feels better when the dew point is lower.

But I don’t get why, or what it is. What is the dew point, and why does it feel so good when it’s low?

Well, first of all, dew point is just a great measure of how it’s going to feel outside. I think temperature is just as important with humidity, but relative humidity, like the relative humidity that’s on our weather apps, is just a total crock. Because it’s not — it’s literally relative to the temperature, so it’s not helpful.

Okay, say more.

Relative humidity doesn’t help me fully understand what it’s going to feel like outside. Whereas the dew point, in a very basic sense: It’s the amount of moisture in the atmosphere.

A close-up photo of Rafael Nadal shows the tennis player’s face in profile, looking down at the court. He wears a purple T-shirt and a bright pink headband, and his dark hair is soaked with sweat that drips down from all over his face, a large droplet falling from his chin.
This is a picture of Rafael Nadal from the US Open a couple of weeks ago. Look how much he is sweating! I have no idea why the US Open is played during the hottest and steamiest part of August.
Eduardo Munoz Alvarez/VIEWpress

The higher the dew point is, the greater the amount of moisture in the air. And so when the dew point is higher, the air is holding more moisture content and it feels more uncomfortable. When the dew point is lower, obviously, there’s less moisture in the air, and it feels more comfortable to be outside in general. The other threshold is when the dew point gets too low, when it’s too dry, and that’s when you have chapped lips instantly, and it’s wintertime.

That’s when you have to turn on the humidifier.

Exactly. But there’s definitely a “Goldilocks zone” where the dew point is, like, 55°. 50° to 60° is generally pretty, pretty perfect. It just feels pretty great out there.

I always like to think about this: If the dew point is 75° but your temperature is 100°, your relative humidity is going to be low, because relative humidity is calculating the relationship between the temperature and the dew point. But you and I both know, because we know dew point, it’s going to be hot as heck out there.

Based on what you’re saying to me, and based on my very elementary knowledge of the dew point, my calculation is that that sounds extremely disgusting.

Okay, so I did the calculation. If you have a temperature of 100° and a dew point of 75°, that would give you a relative humidity of around 45 percent. So if I checked nothing but the relative humidity, I’d be like, “Oh, it’s 45 percent.” If I go outside, I will just be hit by this wall of death and sweat.

“45 percent relative humidity” in my chicken weather brain would sound like a dry heat. I don’t mind a dry heat — Arizona is fine!

And we’d be so wrong. I use the dew point alone, because it’s a standalone measure of how much moisture is in the atmosphere. When the dew point is at 75°, everyone knows that it’s going to feel terrible. And so that’s the real value of the dew point.

It’s like a language to alert everyone that it’s going to be horrific outside.

I’m of a firm belief that not all 72° temperatures are created equal. The 72° in fall feels a lot different than the 72° in spring and the 72° in summer. My hunch is that this has to do with the dew point.

Well, I think it’s also a lot of perception. We perceive things differently. When you come out of winter, into spring, and you get the first kind of hot day, I really feel that 70° is gonna feel a lot different than the 70° will in August. That’s a whole other discussion.

But forget the month. If you have a temperature of 75° and your dew point is 40°, it’s going to feel nice outside. The dew point is low, the temperature is 75°. And it’s a beautiful day. If it’s 75° outside with the dew point at 72°, you’re going to feel like you’re in a sauna because the dew point is so high.

Let’s say we only look at the dew point to plan our day: What information might we be missing, and are we cool with missing that?

I like to say that the dew point is only one piece of the puzzle. For one thing, the dew point can change dramatically throughout the day. It can be a miserable 75°F in the morning, only to drop into the comfortable 50s thanks to an afternoon cold front. But more importantly, the dew point is just one piece of information in a larger picture. There are so many different intricacies to the weather that decide how it feels outside: Temperature, dew point, wind, clouds, precipitation. While dew point is important, it’s also important to look at it in the proper context.

I want to zoom out a little bit and ask you about your vibe calculation. What factors into a good weather vibe and what factors into a bad weather vibe? It’s subjective, but is it relative?

To me, what I try to hold strong to is the idea of what a perfect weather day is, and to me those days are, you know, upper 60s to the 70s temperatures, low dew points, a nice wind and lots of sun, and we don’t want clouds or rain — those bring the numbers down.

You don’t want too much wind, where it’s uncomfortable and annoying to be outside. And obviously you don’t want it to be too hot, too cold, or too humid.

I feel like there’s this Goldilocks zone of 70s temperatures and 50s dew points, which is kind of like the perfect day. But you’re right. There’s definitely some days in winter and summer that kind of become a judgment call.

A long view shows a wide stretch of light sand California beach on a sunny day with small, faraway beachgoers along the edge, curving around a calm blue Pacific Ocean bay filled with small boats just offshore. In the background, mountains rise into an intensely blue sky.
This is Santa Barbara, California. This is where some of the most perfect weather exists. Nancy Meyers wouldn’t set a movie (It’s Complicated) here if it wasn’t perfect.
Tayfun Coskun/Anadolu Agency via Getty Images

But I try my very best to remain as unbiased as possible and stick to the original idea, which is that there is a perfect weather day in New York. Those are the only ones that I can give a perfect rating. And then there’s a worst-case weather day in New York, which is our only ever 0 out of 10, which was last year during the floods in September — the remnants of Hurricane Ida.

There’s definitely a formula for what the perfect day is. There’s some differences individually too. And it changes by the season a little bit.

You mentioned that you try to be balanced and unbiased. And I think we got that earlier when you said, “Oh, yeah, we need the rain.” Rain obviously has bad vibes and lower numbers, but if we need it, do you make a note of it?

The weather vibe is separate from the need, you know? Because if we start rating weather based on all these outside influences, then the rating is not the true rating anymore.

Yeah, I get it. If we got that weird 80° day in the middle of winter, I’m sure that will score good vibes — but you’re probably thinking of climate change and how this is actually kind of concerning.

I mean, I’ve gotten that from people. There were a couple of days last year where it was warm out during the winter. It was in February, and someone replied, “You know, just me enjoying the end of the world in my sunglasses.”

But if you’re rating the weather and you start adjusting the rating based on outside influences like that, you’re getting into a really complicated zone where you have to think about climate change or drought.

Basically your rating isn’t a treatise on climate change. It’s just about whether there are good vibes or bad vibes outside today.

Exactly. It’s like, am I gonna have a good time? Or am I gonna have a bad time out there? That’s pretty much it. I always say to people that the way that I try to look at it is: When I step outside, how am I going to feel? Am I going to be miserable?

When you go out to get a coffee, or you go to work, or when you get on the subway, what are you going to feel? What’s the vibe of the day? I try to keep it simple in that sense.

Update, August 2, 2023, 11:25 am ET: This story was originally published on September 16, 2022, and has been updated to include the record temperatures of summer 2023.