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When folks grumble about feeling uncomfortable in July, they often say, “It’s not the heat; it’s the humidity.” And sure, it’s humid—but the dewpoint is what tells you how muggy and sticky the air feels. Whether you’re tending your garden, heading out for a run, or just trying to survive a summer day, let’s break down what humidity means—and why dewpoint matters more than you might think.
As soon as you wake up in the morning, you can get a good sense of how humid it is outside—just by looking at the sky out your window. No weather apps needed. Read the sky:
Deep blue sky: This means the air is dry. You’ll often see this kind of clear, rich blue on crisp, cool days or in places with low humidity like Montana.
Light blue sky with a nearly white horizon: This shows average humidity. The air holds some moisture, but it’s nothing too sticky or uncomfortable.
Milky or hazy sky: This is a sign of very humid air, which is common in summer in places like the Carolinas and the Gulf States. That whitish haze happens because there’s so much moisture floating in the air.
You know that sticky feeling on a hot summer day—when you practically peel yourself off vinyl car seats or the laundry just won’t dry on the line? That’s humidity at work. It comes from water vapor, which is invisible moisture floating around in the air.
There are a couple of ways to measure how much moisture is in the air—but let’s focus on the two most common ones:
1. Relative Humidity (What You Usually See on Weather Apps)
This is the one most people are familiar with because it shows up in your phone’s weather forecast. It’s a percentage that tells you how close the air is to being “full” of moisture.
For example:
If the relative humidity is 100%, the air is completely saturated—any more moisture, and you’ll get dew, fog, or rain.
If it’s 60%, the air is a little over halfway full.
But here’s the catch: relative humidity changes depending on the temperature. Warmer air can hold more moisture than cooler air, so the same amount of water vapor might feel humid in the morning but drier in the afternoon.
That’s why meteorologists often prefer another measurement…
2. Dewpoint (A Better Way to Tell How Humid It Feels)
While weather apps usually show relative humidity, dewpoint is actually a better way to tell how humid or muggy it feels outside.
So what is it? The dewpoint is the temperature at which the air becomes so full of moisture that it can’t hold any more—and water starts to condense into dew, fog, or even rain. It’s measured in degrees, just like temperature.
But here’s the key difference: Dewpoint doesn’t change just because the temperature goes up or down. It reflects the actual amount of moisture in the air. So it’s a much more reliable way to judge how humid the day really is.
Dewdrops on grass.
Why Dewpoint Feels More Accurate
Let’s say it’s 68°F in the early morning, and the air is completely saturated. The relative humidity is 100%, and the dewpoint is also 68°F. You might see dew on the grass or fog in the air.
Later in the day, the temperature rises to 90°F. The air can now hold more moisture, so the relative humidity drops to 50%—but the dewpoint stays at 68°F, because the amount of moisture hasn’t changed.
That’s why dewpoint is the go-to measurement for meteorologists and weather nerds—it gives you the real story about how sticky or dry the air feels, no matter the time of day.
Whew! We’re guessing the dewpoint is over 65°F! Credit: Shutterstock
Dewpoint Comfort Levels
Here’s a quick cheat sheet to help you understand what dewpoint numbers feel like:
65°F and above: Very humid—feels sticky and heavy.
Low 60s: Somewhat humid—you might notice the moisture, but it’s manageable.
50s: Comfortable—most people feel good in this range.
40s and below: Dry and crisp—think of cool mountain air.
If you want to know whether you’ll be sweating through your shirt or enjoying a pleasant breeze, check the dewpoint, not just the temperature.
Dewpoint Can Even Predict How Cool the Night Will Be
Here’s a neat trick: the dewpoint can help you guess the lowest temperature overnight.
Air can’t cool down below the dewpoint without something big changing—like a new air mass moving in. That’s because once the air cools to the dewpoint, moisture starts to condense into dew or fog. This process releases a little bit of heat into the air, which actually slows down further cooling.
So, if the dewpoint is 60°F in the evening, chances are the overnight low will stay right around 60°F—not much lower.
This is super handy for planning:
Want to know if you’ll need a jacket by morning?
Wondering if the tomatoes will get hit with a cold snap?
Check the dewpoint. It’s not just about muggy afternoons—it’s also a quiet clue to how the night will feel.
Wrapping It Up: Know Your Dewpoint, Know Your Comfort
Now you know—it’s not just the temperature or the humidity making you sweat. It’s the dewpoint that really tells the story. By learning to read dewpoint ranges and what they mean, you’ll get a much clearer sense of what’s going on in the air around you.
Whether you’re planning a hike, working in the garden, or just trying to stay cool, keeping an eye on the dewpoint can help you stay one step ahead of those muggy summer days.
Want to take your weather savvy a step further? Check out our Heat Index Chart to see how temperature and humidity combine to affect how hot it really feels outside.
Catherine Boeckmann loves nature, stargazing, and gardening so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann
Being in the south, Alabama, 20 miles from the Gulf, as the article mentions, it's very humid in the summer. As the saying goes, you can cut the air with a knife. Knowing the humidity makes the air very uncomfortable. Curiosity, I bought gages with both the temp and relative humidity readings. Having three of them, they all were within 1-2 degrees, so were fairly accurate it seemed. I have charts that notes the Heat Index for various readings as OFA also has. But many times the Heat Index is off the chart(s). Searching the NET found a web site that inserting the temp and
humidity it instantly gives the Heat Index. From NOAA https://www.wpc.ncep.noaa.gov/html/heatindex.shtml It's a fun site. One table is for Dew Point and another is for Relative Humidity.
To make matters more confusing, I found a site showing the formula to determine the Heat Index, quite complicated. From the National Weather Service: https://www.weather.gov/ama/heatindex
A sampling of my record keeping My Codes:
FS = Full Sun, gage placement
PS = Partial Sun
OC = Over Cast
HI = Heat Index Temp (from chart) degrees
HM = Humidity
HD = Heat of Day @ 2:00 pm
OT = Outside Temp
IT = Inside Temp
7/07 OT FS HD 115 F HM 90% HI = off the chart HI = 151 degs (per the input table)
Ready for winter. The south may be hot, but in Vermont 2 or 3 years ago it was 104 in the shade.
Hate the summers heat and humidity. I'm already counting down the days for Fall and my favorite season Winter. I'm much more comfortable in colder weather than summer. Now I'm very irritable, sluggish, can't breathe, loose weight from lack of eating. For those who love summertime heat,you can have this horrible heat I'm praying for the quick end of summer.
Good morning Bob! Thanks for another good article! The dew points in Houston have been in the high 70s almost all summer, each morning it is 79° and I have seen several handfuls of 80°and 81° dew point readings. I’ve lived here all my life and it seems like this summer has been the worst. Even five years ago our dew points rarely got above 76. I’m not sure what the change is, but I don’t like it! So many people don’t even know what I’m talking about when I mention this reading, so I’m going to send them your article! Happy stargazing and I hope you have clear skies for Mars viewing!