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Heat & Humidity Can Be Uncomfortable But It’s Those High Dew Points That Make You Miserable

Learn why the dew point reading is the one to watch!

Summer weather is in full force. Thunderstorms, rising heat indices, and the 3H’s—hazy, hot, and humid—can send you packing straight to the beach or pool. But while heat and humidity are certainly major players in summer-like conditions, it’s really those dew point readings your meteorologist talks about that really play a key role in your comfort during the warm weather.

What’s the Difference Between Humidity and Dew Point?

Humidity and dew point are two terms used regularly by your meteorologist during your local forecast, but they are not interchangeable. They each refer to different things when it comes to measuring moisture in the air. Humidity, or “relative humidity,” measures the percentage of water vapor in the air. So if it’s 97% relative humidity outside, that means the air only needs 3% more water vapor to achieve complete saturation of 100% (total air saturation = fog. Many people believe 100% saturation = rain, but fog is what forms in 100% relative humidity).

A hygrometer measures moisture in the air.

However, knowing the humidity percentage doesn’t tell the whole story on these summer days. The dew point is a better indicator of how sticky it feels outside. While we may say, “boy, it’s humid out!” chances are, what we’re really feeling is a high dew point. Even if you enjoy the warm temperatures of summer weather, a high dew point temperature–usually anything over 60º Fahrenheit — feels downright miserable for just about everyone.

Meteorologists like to use dew point because it shows a better picture of the relationship of relative humidity to air temperature. Dew point’s definition is, literally, the temperature at which dew forms, or the temperature the air has to cool at constant pressure to reach total saturation.

The Lemonade Test

Iced Tea - Lemonade

Take a look at that glass of ice cold lemonade that’s leaving a messy ring of moisture on your patio table—it tells us a lot. It means the ice has actually cooled the glass and the liquid inside down to or below the dew point, so any moisture that’s in the air condenses on the glass. When dew points are low, that glass of lemonade isn’t as sweaty and you’ll notice your towels drying much faster on the clothesline.

While it’s true that the dew point is not a directly measurable parameter, your home weather station can now give dew point readings.

Dew Point Readings

overheated woman fanning herself with an orange fan.

40º-50º – Dry; nice and comfortable.
60º – Getting uncomfortable.
70º – Oppressive!

The current dew point can be calculated using the air temperature and a relative humidity value, (which is measured using something called a sling psychrometer) – but you don’t have to do the math—this dew point calculator figures out values for you! Have fun!

Your best defense in the oppressive heat is to ratchet up the A/C to high and wait for a thunderstorm to usher in some drier air.

Susan Higgins is the Farmers' Almanac's Web Content Editor & Social Media Manager. She is a freelance writer/editor, copywriter, blogger, and writer of short fiction. Her passions are advertising, cooking, the ocean, libraries, pets & animal welfare, Netflix binges, and finding the perfect book at her local library.

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Mark Bose

Osteoarthritis for 30 years, 27 invasive back procedures, titanium rods the latest. I would have to say the changing weather; (.08) dew point/∆temp. x BarPr= a ship load of hurt.
Still on the right side of the grass though soo…is there a place I can move were the weather doesn’t change? Probably a place not good for Farmers Almanac sales but I’ll gladly sign up for annual renewal for right answer;) God Bless all. M

Deb

I know this is right about the humidity and the dew point. I also know that when it gets hot the heat does bother too. I have been in desert weather and even though the heat is dry heat, it is like walking into an oven.

Jan

I have rheumatoid arthritis (since my teen years–now 61) and I have found that the dew point is the key to how much pain and inflammation I experience. It is key to how I feel during the summer. Most think that to move to a warm climate is the answer to living with RA but for me, the colder the climate, the better I feel. I belong in Alaska, I think. :o)

Deb

‘@Darlene,

I use accuweather which provides all you need to know. http://www.accuweather.com/en/browse-locations

just adjust for your location.

darlene macneal

HATE, HATE THE HIGH HUMIDITY!!!!!!!!!!!!!!!!!!!!! DEWPOINT—–FOLLOW IT CLOSELY!!! AND THE WEATHER STATIONS RARILY SAY WHAT THE DEWPOINT IS!!!! I HAVE AN OLD SCANNER THAT I LISTEN TO THE WEATHER ETC. ON!!!!!!!!!!!!!

Raymond Guinter

can you explain how they figure the wind chill number? I know it has something to do with wind speed and temp. But how is it calculated?

Deb

The humidity this summer has been miserable to deal with. In the news today parts Newfoundland, Canada are dealing record breaking numbers.

http://www.cbc.ca/news/canada/newfoundland-labrador/temperature-humidex-values-set-to-approach-all-time-highs-1.2722464

“CBC Meteorologist Ryan Snoddon said it’s lining up to be a record-breaking couple of days, with temperatures forecast near 30 C, and a humidex near 40.

“The July 30 record of 27.8 C set back in 1967 is sure to fall today,” he said.

“Tomorrow’s July 31 record of 29.3 C, set back in 2004, will also likely be broken.”

Snoddon said the 30-degree mark at the St. John’s weather station is tough to come by — it has reached that mark just nine times over the past 72 years. “

dUe date

My Maine newspaper’s almanac failed to mention that today is John Glenn’s 92nd birthday. As a native Ohioan I’m offended by this TYRANNY!

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