Summer Survival | It’s All About Dew Point – Not The Humidity

sticky muggy dew point

Dew point is what it’s all about during the summer. When it comes to the forecast, mostly what I want to know is the dew point.

Why? Because that’s directly related to how “muggy” or “sticky” it feels.

The relative humidity tells me nothing. Well, it does, although it doesn’t mean much regarding my summer comfort level. Here’s why:

First, there are three typical numbers in a summer forecast:

  • Temperature
  • Relative Humidity
  • Dew point

Temperature is straight forward. It’s simply the temperature. 70 feels nice. 80 it’s getting hot. 90 it’s hot. 100 it’s extremely hot. Simple, right?

Relative Humidity is the least useful, and can be very misleading. I might best illustrate this by showing you a chart.

TimeTemp.RHDP
8:00 AM7287%68
10:00 AM7482%68
12:00 PM7871%68
2:00 PM8458%70

For those who focus on the relative humidity, they would be wrong to conclude that the weather will be the most comfortable at 2 PM ( ‘only’ 58% humidity).

In fact, the most miserable time of the day would be 2 PM! Why? because the dew point is 70, not to mention that the air temperature itself is the hottest of the day at 84 in this example.

If I stepped outside at 8 AM, though the relative humidity is high at 87%, the air temperature is a comfortable 72, even though the dew point is on the muggy side at 68.

(here’s a DP calculator that I found online)

Dew Point Is How Muggy It Feels

It’s the temperature at which water vapor in the air will begin condensing to form dew on the grass, or mist and fog in the air.

It is an indicator of the total amount of moisture in the air and an important comfort factor (or lack thereof!) during the warmer summer months.

When you sweat / perspire, the moisture on your skin evaporates and cools your body. When the dew point is high, the water on your skin evaporates very slowly because there’s so much water vapor in the air. You don’t get the efficient cooling effect on perspiring wet skin with ‘wet’ air. It feels “muggy” or “sticky”.

Dew points less than 60 degrees feel comfortable or “dry”. When it rises above 65 degrees the air feels “sticky.”  As it climbs into the 70s the air becomes very sticky or oppressive.

Dew Point versus Relative Humidity

The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.

The higher the dew point rises, the greater the amount of moisture in the air. This directly affects how “comfortable” it will feel outside. Many times, relative humidity can be misleading. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. It would feel much more “humid” on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.

So if you want a real judge of just how “dry” or “humid” it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

National Weather Service

The Takeaway

To sum it up, I don’t care what the relative humidity number is during the summer. Rather, among other things, I want to know what the dew point is going to be that day, along with the high temperature! That way I’ll know how yucky it’s going to be outside!

How muggy does it get where you live during the summer? What are your typical summer dew point temperatures? When does it feel really nasty to you? Do you actually get used to it? Any secret tips for staying “not so hot” outside during these conditions?

As I write this it’s mid July in northern NH. I’m looking at my weather station which indicates a DP of 65 degrees right now at noon (air temp. a pleasant 77). Feels muggy, though not terribly awful like hitting high 60s and 70+ dew points.

Indoor Humidity Level During Winter – What’s Best?

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25 Comments

  1. How do you find out the dew point? It’s 69% now at 80d, very muggy, and we are heading for 90+ in several hours.

    1. Chevy, I linked to a dew point calculator in the article which you can use to play around with the numbers.

      That said, a good weather forecaster (e.g. your local TV weather) will regularly talk about the dew point expectations for the day (during summer). If they don’t, well, that’s not being very informative.

      1. Dew point is not addressed in our reports, just humidity.. will look at article deeper and check out the link. Is now 97 degrees in our covered( with heavy fiber glass reflective) chicken run.( chickens are under the fence line/trees in the dirt.) . Local weather says only 91 in our town..also says Heat index is 105….humidity 63% .
        No they are not very informative, what one gets when NOT in city..It is what it is.. guess i need to put up a weather station outside but has not happened.Not at top of list.

      2. Our local weather doesn’t have DP. Lacking access to the internet, is there anyway of determining DP if all I had was a thermometer and some other non-electric device? Like if I’m in the woods?

  2. the dew point around here can very wildly

    the dew point here can and does go from in the 50s to the upper 70s

    this is in west ny state ive seen it bone dry and as low as in the 40s to the 70s in 24 hours

    tomorrow and saturday the temp is gonna be in mid 90s and a dew point in the mid 70s

    in other words BRUTAL

  3. Live in North Central Florida and love me some humid weather. Keeps the Yankees away all summer

  4. Ken (and all),

    NRP put me on to a site called Ventusky dot com. Up to the minute weather readings anywhere in the country (world?).

    Just checked readings at my location. Temp 86, perceived temp 98, humidity 70%, dew point 75.
    Great site.

    1. Awesome! Temp 70. Perceived temp 60. Relative humidity 10%. Dew point 19 degrees F.

      I 💘 that “muggy” isn’t a word that I use often, at least since I left New England for the mountains of Colorado.

    2. Dennis;
      Yeppers, great site, all kinds of information there, even the Upper Atmosphere weather.

  5. – 4 PM 7/18 96° 0% (chance of rain) 26% S 15 MPH ; That’s copied from what the local weatherman is giving as our weather hereabouts. Just for what it’s worth, everyone is complaining how humid it is. It all depends on what you are used to. (Welcome to West Texas)
    – Papa S.

  6. Yes yes
    A coworker decided to correct me the other day after I said it was humid and muggy that morning when I ran.
    I guess he didn’t know that a flurry of corrective meteorology terms after sweating my guts out in my language translates to “you wanna wrestle” and apparently he didn’t know the safe word.

  7. Not a meteorologist and dew point is not given often. I do remember east coast Virginia in the summer as a child. Awake most of the nights flipping my pillow over trying to find a cool side to put my head on.

    Stationed in Fort Huachuca, AZ in the late 1970s and had a clothes line with one line. It was so dry that by the time you got to the end of the line the clothes at the beginning were dry. !05 was comfortable because you didn’t sweat, it evaporated as it you perspired. We did drink a lot!

    Now just plain nice outside in the mid 70s.

  8. Advice for Keeping cool no matter where you are.

    Wear a sweat wicking bandanna to keep the sweat out of your eyes.
    I use headsweats: see on amazon, works great!

    Headsweats

    Also then find yourself a tall shade tree post-up under it during the day and get yourself a cool glass of burbon for sippin.
    Cheers!

  9. If you must spend time outdoors in the heat, perhaps a “cooling towel” would be of benefit in order to help stay cool.

  10. Temp here = 96
    Humidity is at 17%
    Due (edit: Dew) Point = 45

    Ya gata love the High Desert hehehehe

    1. Hey NRP

      You just gotta love the rainforest bottomland too:

      Temp = 63F
      Humidity = 80%
      Dew point = 56.7

      Lovely, comfortable day

  11. Hope all MSB friends and family stay weather safe today.

    (It’s 56F here and the morning mist is lifting. About normal for July.)

  12. The dew point is very important to understand for another reason: violent storms! Tornadoes are far more likely when the dew point is high at the same time the temperatures are too!

  13. Exactly. I really like my weather stations. The only thing I hate about them is once the temp hits 80 the dewpoint is no longer available. It shows the “real feel”. When the dewpoint is 60 degrees I may feel a little sticky but ok. Once the depoint hits upper 60’s to 70, I would rather not go outside. It is horrible for me. I can sit in a chair doing nothing and sweat like crazy. So, if the temp is 90 and the dewpoint is 60 I’ll go out and get some things done. Now if the temp is 90 and the dewpoint is 70, if I don’t have to go out, I won’t. I will sit in my air conditioned house and watch tv. For me, the “real feel” is ridiculous information. I want exact information. I want to know what the dewpoint is at all times.

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