When a 72-degree day feels like my armpits are swampy, I begin to realize that everything I ever thought I understood about the weather, especially the temperature, was a lie. I sweat through my shirt, wipe my eyebrows, and stare in disbelief at my weather app, asking, “How can this be the 72-degree FI I know and love?”
Fortunately, I found a better number to tell me what it would be like to be outside—not the relative humidity, which is also a hoax. It is the dew point.
The lower it is – ideally in the 50s to 60s – the less sticky it will feel. The higher it is (the seventies), the closer I get to personal hell. (Relative humidity, a common measure sometimes, measures the dew point against temperature, making it particularly unhelpful on very hot days, when the temperature is well above the relatively low dew point, but still uncomfortable.)
In an effort to explain why a dew point is the best way to tell the weather and what it exactly means, I spoke with John Hominouk on an uncomfortably rainy, sweaty afternoon. Homenuk, who studied meteorology at Keene University, is a dew point enthusiast and the reason I know about dew point forecasts in the first place. It is the power behind New York metro weather Twitter account.
New York Metro Weather has over 58,000 followers looking to it to answer a really simple question: Will the weather in New York City today be good or bad? Homenuk gives its followers a lively rating out of 10 (sunny, moisture-free days score the highest) and sprinkles in a brief explanation of why it will or may not be a fun day in New York.
As Homenuk assured me, not all 72 degrees Fahrenheit days are equal — and the dew point might be the best explanation for that.
It is my pleasure to speak with you. In your words, feelings in New York are appalling today.
yes. We kind of need it. 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 the actual weather – today definitely two out of five.
I think what makes it smelly is that it’s very sticky on the outside. I feel like I’m in a low heat sauna.
the correct! Such a beautiful rainy cold day.
Yes, and I wanted to ask you why. Feel cooler.
You recently – in large part because of your Twitter feed – turned a dew point. The dew point is high today and you feel disgusted. And I know the weather is better when the dew point is lower.
But I don’t understand why, or what it is. What is the dew point, and why does it feel good when it is low?
Well, first of all, the dew point is just a great gauge of how the outside feels. I think temperature is just as important as humidity, but relative humidity, like the relative humidity found in our weather apps, is just a bowl. Because it’s not – it’s literally related to temperature, so it’s not useful.
Well, say more.
The relative humidity doesn’t help me understand what it would be like to be outside. Whereas the dew point, in a very basic sense: is the amount of moisture in the atmosphere.
The higher the dew point, the greater the amount of moisture in the air. Thus when the dew point is higher, the air retains more moisture content and feels uncomfortable. When the dew point is lower, there is obviously 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, when your lips are instantly chapped, and it’s winter.
This is when you have to turn on the humidifier.
exactly. But there is definitely a “golden zone” where the dew point is, say, 55 degrees. 50 degrees to 60 degrees in general is very beautiful and perfect. It feels so great there.
I always like to think about this: If the dew point is 75 degrees but your temperature is 100 degrees, then the relative humidity will be low, because relative humidity calculates the relationship between temperature and dew point. But you and I know, because we know the dew point, it will be as hot as it is over there.
Based on what you’re telling me, and based on my initial knowledge of the dew point, my calculation is that this sounds very disgusting.
Well, I did the math. If your temperature is 100 degrees and the dew point is 75 degrees, that gives you a relative humidity of about 45 percent. So if I check for nothing but relative humidity, I’ll say, “Oh, it’s 45 percent.” If I go out, this wall of death and sweat will hit me.
The “45 percent relative humidity” in a chicken’s weather brain might sound like dry heat. I don’t mind the dry heat – Arizona is fine!
And we would be very wrong. I use dew point alone, as it is an independent measure of how much moisture is in the atmosphere. When the dew point is at 75 degrees, everyone knows it’s going to feel bad. This is the true value of the dew point.
It’s like language to alert everyone that it’s going to be awful outside.
I firmly believe that not all 72 degrees are created equal. A degree of 72 degrees in the fall looks a lot different than 72 degrees in the spring and 72 degrees in the summer. My hunch is that this has something to do with the dew point.
Well, I think it’s also a lot of realization. We perceive things differently. When you get out of the winter, in the spring, and you get the first kind of hot days, I really feel like 70 degrees is going to feel a lot different than 70 degrees in August. This is a whole other discussion.
But forget the month. If your temperature is 75 degrees and the dew point is 40 degrees, you will feel comfortable outside. The dew point is low, the temperature is 75 degrees. It’s a beautiful day. If the temperature is 75 degrees outside with the dew point at 72 degrees, you will feel like you are in a sauna because the dew point is very high.
Suppose we only look at the dew point to plan our day: what information might we lose, and are we happy to lose it?
I would say that the dew point is only one piece of the puzzle. For one thing, the dew point can change dramatically throughout the day. The temperature can be a miserable 75 degrees Fahrenheit in the morning, only to dip into the comfortable 50s thanks to a cool front in the afternoons. But more importantly, the dew point is just one piece of information in a larger picture. There are many different intricacies of weather that determine how it feels outside: temperature, dew point, wind, clouds, precipitation. While the dew point is important, it is also important to look at it in the appropriate context.
I want to zoom out a bit and ask you about your activity account. What are the factors that lead to good weather and what are the factors that lead to bad weather? It’s subjective, but is it relative?
For me, what I’m trying to stick to is the idea of what a perfect weather day is, and for me, those days are, you know, 60’s to 70’s temperatures, low dew points, nice winds and a lot of sun, and we don’t want clouds or rain – that lowers the numbers .
You don’t want a lot of wind, as being outside can be annoying and inconvenient. And you obviously don’t want it to be too hot, too cold, or too humid.
I feel like there’s this Goldilocks area with 70s temperatures and 50 dew points, which is kind of the perfect day. But you are right. There are certainly some days in winter and summer that this kind of judgment becomes a call to judgment.
But I do my best to stay as unbiased as possible and stick to the original idea that there is a perfect weather day in New York. These are the only ones I can give a perfect rating. And then there’s the worst weather day in New York, which is our only day out of 10, which was last year during the floods in September – Remnants of Hurricane Ida.
There is definitely an equation for what is the perfect day. There are some differences individually as well. It changes a bit with the season.
You mentioned that you are trying to be balanced and unbiased. And I think we got that earlier when I said, “Oh, yeah, we need rain.” Obviously rain has bad vibes and lower numbers, but if we needed it, would you write it down?
Weather ambiance is separate from need, you know? Because if we start classifying the weather based on all these external influences, the classification will no longer be the true classification.
Yes I got it. If we get this weird 80-degree day in the middle of winter, I’m sure it’s going to garner vibes – but you probably think about climate change and how worrisome that is actually.
I mean, I got that from people. There were two days last year where it was warm during the winter. It was February, and someone replied, “You know, I just enjoy the apocalypse with my sunglasses.”
But if you assess the weather and start adjusting the rating based on external influences like that, you’re entering a really complex area where you have to think about climate change or drought.
Basically, your assessment is not a thesis about climate change. It just comes down to whether there are positive vibes or bad vibes out there today.
exactly. It’s like, am I going to have a good time? Or am I going to have a bad time there? That’s pretty much it. I always tell people the way I try to look is: When I go out, how will I feel? Will I be miserable?
When you go out for coffee, or go to work, or when you get on the subway, what do you feel? What is the atmosphere today? I try to keep it simple in that sense.