High dew points breed summer misery
When the dew point is high, the sweat on your body will not evaporate, and the body overheats.
July 21st, 2011
02:15 PM ET

High dew points breed summer misery

What's all the talk about a heat dome causing a heat wave that is blistering the eastern third of the nation? You may have heard your local TV meteorologist talk about a "dome of high pressure" being responsible for this heat wave.

Essentially, a heat dome is just another word for a dome of high pressure that forms south of the polar jet stream, usually during the summer months, in the Northern Hemisphere, said CNN meteorologist Chad Myers.

But why has this heat wave been so severe and deadly?

How many times have you also heard, "It's not the heat, it's the humidity," or, "It's a dry heat"? Believe it or not, the amount of water vapor present in the atmosphere can actually make a huge difference in the severity of a heat wave. The amount of moisture the atmosphere holds affects how severe the heat is to the human body.

Meteorologists use the dew point and the current temperature to calculate the heat index. When a parcel of humid air is cooled at a constant atmospheric pressure, the temperature at which water condenses is called the dew point and the condensed water is called dew. The higher the dew point, the higher the heat index, and the more severe the heat is to the body.

Dew points are downright oppressive when they are over 75 degrees Fahrenheit. By contrast, dew points of 40 to 50 degrees are very comfortable. With dry heat (lower dew point) the body can withstand much higher temperatures because when your body sweats, the sweat evaporates and cools the body. However, if the dew point is high, then the sweat on your body will not evaporate and the body overheats, Myers explained.

A very uncomfortable record dew point of 82 degrees was recorded Tuesday in Minneapolis. This also caused the heat index to reach 118 degrees, tying the record set in 1966 for the highest heat index ever recorded at the Twin Cities. Dew points soared into the 80s in the Midwest on Wednesday, causing heat indices to reach an oppressive 123 degrees Fahrenheit in Council Bluffs, Iowa.

Heat indices this high usually occur near the Gulf of Mexico or the coast of Saudi Arabia near a relatively shallow, tropical body of water where dew points are high. In fact, Dhahran, Saudi Arabia, located near the Persian Gulf, had the highest dew point ever recorded, 93 degrees, in 2003.

The unusually high dew points (in some cases, record all-time high dew points) combined with very warm temperatures is making this heat wave unusually deadly. At least 22 heat-related fatalities have been reported with this heat wave, and that figure will probably increase.

But why are the dew points currently at such high levels? Part of the answer is the record floods experienced this spring in the Midwest. The ground is still saturated, rivers and lakes are out of their banks and all of this water is turning to vapor and being released into the atmosphere. High dew points also are common in the Corn Belt of the upper Mississippi River Valley.

Surprisingly, the high dew points are enhanced by the mature corn itself, drawing water from the saturated soil and releasing it into the atmosphere. This process is what meteorologists call transpiration.

So the next time your neighbor jokingly says "it's not the heat, it is the humidity," that's a fact.

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Filed under: Uncategorized • Weather
soundoff (381 Responses)
  1. Judith

    Global warming is real–get used to it folks. We've been fairly lucky out here in Southern California, as it's been pretty mild, but look at the rest of the country. Also, consider the droughts and dust storms here and abroad. Those ostrich like deniers will continue to deny, but I'm afraid this is real climate change. Overpopulation and increased carbon emissions in China will only make it worse. Welcome to our flat, hot and crowded planet.

    July 22, 2011 at 6:19 pm | Report abuse |
    • Trebec

      Shut up. You're still gonna use your computer, drive your car and use your ipod, so even if it was true you would be part of the problem.

      July 22, 2011 at 6:30 pm | Report abuse |
    • woobie

      yeah. thats why chile is buried under 8 feet of snow. there is no such thing as global warming its a lie

      July 22, 2011 at 7:23 pm | Report abuse |
    • Alexander

      Judith is absolutely correct. As for Trebec and woobie you two are ignorant and know nothing about Global Warming. Not only does it make summer hotter, but it makes the winters colder. When you have higher temperatures you also get colder ones. This is what cause the increase in natural disasters because the influx of temperatures are greater. The more temperature change the more severe weather and natural disasters occur. You can reduce your carbon foot print without giving up on technology.

      July 22, 2011 at 8:00 pm | Report abuse |
    • InvestInPublicSchools

      Judith is a perfect example of how our school systems have failed us.

      July 22, 2011 at 8:47 pm | Report abuse |
    • Duce

      Global Warming, "climate change", whatever you want to call it, IT'S REAL FOLKS! It's hard to believe that people write off factual data so easily in support of what some opinionated individual on TV or the radio says...

      July 22, 2011 at 8:49 pm | Report abuse |
    • Duce

      @investinpublicshools – The statement that the world was flat was, more than likely, meant to be satirical.

      July 22, 2011 at 8:52 pm | Report abuse |
    • paul

      Ha in florida its been hitting 100 everyday in the shade. It is nothing for how hot it gets in Texas. How about 30 days of over 116?

      July 22, 2011 at 9:11 pm | Report abuse |
    • Robert

      great job Judith, on the nose.

      July 22, 2011 at 10:29 pm | Report abuse |
    • Bob in Pa

      Give me a break – Global Warming or Climate change. The Earth has been going through this for millions of years without us. Did any of you happen to catch the CNN story last week about the largest explosion on the sun that scientists have ever seen ? These liberal environmentalists think that even the sun can't warm the earth without their help. They must put themselves at the center of evey aspect of life.

      July 22, 2011 at 10:39 pm | Report abuse |
    • KarlB

      The article stated it was due to the high amount of rain received earlier in the year – and that the other highest heat index was recorded in 1966. Global warming – whether true or not – had NOTHING to do with this heat wave.

      July 22, 2011 at 10:47 pm | Report abuse |
    • bassoonist

      Judith and Alexander are right. And I'm disappointed how many people refuse to have an open mind about this. Every country in the world has agreed to the Kyoto protocol to help reduce greenhouse gases except the United States, and we continue to be the leading contributor of this problem. Now, I'm not demanding that you agree with me. I'm just asking you, please, look at the evidence before you make a judgement.

      July 22, 2011 at 11:05 pm | Report abuse |
    • D-Nice

      woobie – You do understand that it's winter in the southern hemisphere, right? Weather volitility is also a side effect of global warming. Maybe you should do a little research before you make a fool of yourself on CNN.

      July 23, 2011 at 12:30 am | Report abuse |
    • Jay


      About 40 years ago, people were shouting the same ideas that you are, except the opposite. People thought the world was going to freeze. Yes our planet is crowded, and yes we use up resources, but problem is we need those to sustain life. Do I personally believe the use of resources and population is linked? Maybe very little of it is linked to heat, not many people can say theyve lived long enough to witness three earth weather cycles., but its fact the earth go through cycle as written history shows.

      July 23, 2011 at 2:08 am | Report abuse |
    • Santiago de Chile

      carbon emisions in china? I really think you don´t have to go that far... just the USA alone is generating 33.3% of ALL carbon emisions of the whole world! ...also if every country consumed equally to what the USA consumes... WE WOULD NEED 4 to 5 PLANETS!!!!
      so please Do Not talk to me about china...

      July 23, 2011 at 2:11 am | Report abuse |
    • Various Authors

      You know those CFL's the electric company sends out for free without me even asking? How the hell do I throw them away? The garbage men won't take them, too hazardous. I tried using a few but they gave me a headache, and as you can see, they aren't stopping this heat wave. Perhaps if I leave my carbon footprint on someone's ass...

      July 23, 2011 at 7:38 am | Report abuse |
    • studdmuffins

      Gee, surprising that global warming is the cause for plain old summer heat.

      July 23, 2011 at 9:13 am | Report abuse |
    • Idea

      We had a mild and wet spring and summer, but one little heat wave and the climate Nazis come out. Climate changes, and mostly on it's own. It has done this since it's inception. You worried about climate change? Try and make some changes for the better, don't sit on the internet promoting worthless propaganda and fear.

      July 23, 2011 at 10:34 am | Report abuse |
    • Mobius007

      Google the phrase "global warming irreversible"...

      The simple fact is that humanity, by burning coal, oil and other fossil fuels, have released a half-billion years of stored carbon into the atmosphere. The damage is done. There is no political will to reduce carbon emissions, and even if humanity decided to, it’s likely already too late to change the outcome.

      The good news? We'll only experience a small taste of what's to come in our lifetimes. Future generations will be the ones who have to struggle through the disaster they have inherited.

      July 23, 2011 at 10:45 am | Report abuse |
    • OldGoat

      Lessee...we have about 140 years of scientifically collected weather data from which the global warming nuts are extrapolating millions of years of climate patterns and coming to an unscientific conclusion. Judith and her ilk are a bunch of Chicken Littles running around and screaming that the sky is falling, without any positive evidence to back such a claim.

      July 23, 2011 at 11:31 am | Report abuse |
    • Rock

      Judith in High School Biology we learn the difference between weather and climate. Overall, yes the temperature of the planet is increasing over time. The heat this year cannot be used as empirical evidence to support you claim however, becuase it is merely the weather....not climate.

      July 23, 2011 at 12:54 pm | Report abuse |
    • Mbrady

      love the global warmers that were so busy claiming the seas will rise 10 feet, yada yada yada. yet when the CORRECT data for global temperatures came out, and everyone found out that the "scientists" padding numbers, no one said much anymore. al gore won an oscar for a INACCURATE movie and yet has never said that he would fix his "data."

      I didn't realize that there were digital thermometers 100 years ago were so accurate so that the weather people can go on their local news and say that "we broke a record that stood since 1895."

      sure maybe the earth is getting a little warmer but no one wants to admit that it's cyclic rise and fall of temperatures. all the chicken little, the sky is falling people are looking at the last 50 years of temperatures, and "oh my god" – it's global warming. maybe you people should look at the average temperatures over the last 100,000 years and let us all know how many times the earth has warmed up and then cooled off.

      July 23, 2011 at 12:57 pm | Report abuse |
    • Dave

      The real 'inconvenient truth' is that we are currently in a period of global cooling. But, that fact isn't front page news, doesn't sell newspapers, and isn't named Al Gore. It's just actually based on real data vice the data created to make the point of the people who have a point to make. Now, I firmly believe that humans are contributing to the overall system and there is no doubt in my mind that human activity has a, perhaps arguably, large impact compared to other factors. Just because it's hot this summer to folks in the middle of the US, DOESN"T mean the average world temp has risen. The weather is a local situation caused by global patterns. But, we're talking about the wrong things here! What we need to be talking about is creating sustainable power sources. That's it! It really is simple! We WILL run out of fossil fuels some day. They are not infinite. We need power sources that are sustainable. And, guess what, f we have those, they WILL OF NECESSITY be clean (or much cleaner). And, if they are, then guess what, our impact on the environment will stabilize. If the only reason we keep talking about 'global warming' is because we're trying to find some way to convince ourselves to stop screwing up the planet, well, whatever it takes. Let's just keep our eye on the ball – it really is quite simple – get off fossil fuels BEFORE we HAVE to – and the rest will take care of itself.

      July 23, 2011 at 1:21 pm | Report abuse |
    • yo

      woobie, chile is in the andes mountains. shut up and learn your geography. what kind of name is woobie anyway?

      July 23, 2011 at 1:24 pm | Report abuse |
    • Mobius007

      Dave said, "The real 'inconvenient truth' is that we are currently in a period of global cooling. But, that fact isn't front page news, doesn't sell newspapers, and isn't named Al Gore. It's just actually based on real data vice the data created to make the point of the people who have a point to make... But, we're talking about the wrong things here! What we need to be talking about is creating sustainable power sources. That's it! It really is simple! We WILL run out of fossil fuels some day. They are not infinite. We need power sources that are sustainable. "

      Dave, given your irrefutable "facts" that we are in a period of global cooling, it makes much more sense to abandon renewable energy entirely and consume fossil fuels at an increased rate. We can thus release as much CO2 into the atmosphere as possible, offsetting your scientifically proven global cooling trend.

      Based on your facts related to global cooling, renewable energy is actually a threat to mankind.


      July 23, 2011 at 5:13 pm | Report abuse |
  2. oskar

    WOOBIE, got news for you...Chile is in the SOUTHER HEMISPHERE where its WINTER!!!!!
    Idiot, stop listening to Rush and get real news with some truth.

    July 22, 2011 at 8:06 pm | Report abuse |
    • bry562bry5

      i would advise you to do the same thing.

      July 22, 2011 at 8:51 pm | Report abuse |
    • josh

      not to start a fight, i personally don't belive in global warming but how do you know your information is the truth.

      July 22, 2011 at 9:53 pm | Report abuse |
    • bassoonist


      July 22, 2011 at 11:19 pm | Report abuse |
  3. julianpenrod

    Twice I tried to place a comment on this subject. It didn't have invocations to violence, it didn't bad mouth anyone, it didn't use suggestive language or vulgarity. It did mention chemtrails and it pointed out that there are many factors that make up "the air", including qualities that aren't generally mentioned yet. I was going to say that the air is being changed in ways many people don't even realize is possible and so they think the warmth is "normal" or that it's even "warmth" and not, say, the inability of air even to absorb heat anymore. But CNN refused to place those comments. So much for freedom of spech. New World Order quislings will opine that, "This is their company and they have the right to do whatever they want with it! There is not freedom of speech on private property, only on public property!" But freedom of speech is more than just a legal guarantee. It's a principle. It seeks and welcomes meaningful ideas, in the hopes that they might hold the key to improving the world. Whoever so wantonly abridges free speech is deliberately foregoing what could make things better! It may be legal, but it is an exercise in unethicality and lack of principle!

    July 22, 2011 at 8:29 pm | Report abuse |
    • Bugmenot

      And your point is?

      July 22, 2011 at 9:43 pm | Report abuse |
    • Joe

      Chemtrails? New World Order?


      oh wait. you're serious.

      let me laugh harder.

      July 23, 2011 at 12:57 am | Report abuse |
    • Various Authors


      July 23, 2011 at 7:34 am | Report abuse |
  4. Michael

    It amazes me how many people still don't realize global warming has nothing to do with temperature. Global warming is a measure of climate change over time influenced by industrialization. You can't say "oh we're having a blizzard in the winter, global warming is false ... " or "ooh we're having a heat wave, global warming." What you can look at is how the climate of the individual seasons have changed over the decades.

    July 22, 2011 at 11:48 pm | Report abuse |
    • Idea

      The "Climate" has been fluctuating for millions of years! Just because we are comfortable in our own little bubbles doesn't mean that the Earth doesn't change. Keep throwing out your fears and you'll be rewarded with some BS Cap and trade bill. Be careful for what you wish for.

      July 23, 2011 at 10:41 am | Report abuse |
    • OldGoat

      The global warming nuts are attempting to extrapolate millions of years of climate patterns from about 140 years of scientifically collected weather data. It's junk science.

      July 23, 2011 at 11:34 am | Report abuse |
  5. Kuwait

    You think that is hot, I am in Kuwait on deployment and it hits 120 everyday. Plus it is humid so it feels like 140

    July 23, 2011 at 1:29 am | Report abuse |
    • Kate65

      Thank you for wearing your country's uniform. Stay safe.

      July 23, 2011 at 2:23 am | Report abuse |
    • OldGoat

      Not to mention the smell from some of the local residents. Be careful, buddy. We want you to come home safe.

      July 23, 2011 at 11:35 am | Report abuse |
  6. Samdromeda

    Global warming is caused by war and de-vegetation. Each explosion and discharge of guns infuses heat into the atmosphere. The ability of the earth to neutralize the effects of each incident of heat infusion along with record flooding in the USA has manufactured the heat dome. Summer is here and dew points are rising. Welcome to the steam bath. In the areas where we have droughts we have fires. Watch for the expansion of deserts.

    July 23, 2011 at 1:36 am | Report abuse |
    • Think It Through

      War? Really? Wow. War? Each time you start your car, of have a bonfire with your friends or grill food for your family you infuse heat into the atmosphere. Many thing other than war infuse heat into our atmosphere, like the American ran science projects and experiments that they have the right to conduct because WAR kept their freedom... Just saying.

      July 23, 2011 at 2:22 am | Report abuse |
    • OldGoat

      Global warming is caused by war and de-vegetation.
      Not to mention ignoramuses opening their mouths and expelling hot air as they spout nonsense.

      July 23, 2011 at 12:23 pm | Report abuse |
  7. ed

    So is it Climate Change or Global Warming? I haven;t gotten the Gore talking points to know which one it's gonna be this year...

    July 23, 2011 at 1:36 am | Report abuse |
  8. Rich39

    It's always been hot in the summer. 25, 45, 60 years ago we didn't have TV stations telling us how hot it was. Now most people spend over 90% of their time in AC comfort.
    My father got his first AC home when he was 62. Never had a AC car. I got my first AC car when I was 52. I always had a sports car wth no AC. I live in South Carolina. 104-107 yesterday. Sitting in the shade it was 100.
    Get use to hot weather.

    July 23, 2011 at 7:09 am | Report abuse |
  9. copper

    A climate cycle is a type of recurring climate pattern that involves natural cyclic variations in the Earth's surface temperature, as indicated by temperature proxies found in glacier ice, sea bed sediment, tree ring studies or otherwise.
    Several climate cycles have been identified or hypothesized. These range from the cyclic behaviour of the Earth's orbital parameters (called Milankovich cycles) which are reflected in the long-term climatic record spanning several ice ages, through the Atlantic Multidecadal Oscillation, to short cycles such as:
    the El Niño Southern Oscillation
    the Pacific decadal oscillation
    the Interdecadal Pacific Oscillation
    the Arctic oscillation
    the North Atlantic Oscillation
    the North Pacific Oscillation.
    The 11-year Sun spot cycle (the Hale cycle) may also be discernible in the climate record (see Solar variation).
    Climate cycles are popular with media. One example is a 2003 study on the correlation between wheat prices and sunspot numbers.[1]
    There is also the Bond event, a 1,500-year climate cycle claimed from ice core samples, and used in the global warming controversy.
    Other than the Milankovich cycles (and perhaps the Hale cycle), no climate cycle is found to be perfectly periodic and a Fourier analysis of the data does not give a sharp spectrum.
    One difficulty in detecting climate cycles is that the Earth's climate has been changing in non-cyclic ways over most scales of time. For instance, we are now in a period of global warming that seems to be anthropogenic. In a larger time frame, the Earth is emerging from the latest ice age, which means that climate has been changing over the last 15,000 years or so. And the Pleistocene period, dominated by repeated glaciations, has developed out of a more stable climate in the Miocene and Pliocene. All of these changes complicate the task of looking for cyclical behavior in the climate.

    July 23, 2011 at 7:40 am | Report abuse |
    • Caz

      You are right. There are many, many natural cycles, and our understanding of them is in infancy. Any effect of AGW is indistinguishable from the noise of the other, natural cycles. But warm is better than cold, so I say enjoy the heat while we can.

      July 23, 2011 at 12:46 pm | Report abuse |

    Most of these deniers wouldn't know the difference. I don't like putting ignorant people down, but why don't you find out the facts b-4 making claims that you know absolutly nothing about. I guess that it because of lies and missinterpations.You are supporting the rights agenda to eliminate knowledge. remember, a very wise man once said, "beleive nothing of what you hear and only hafe of what you see. of course, that would eliminate B.S. radio.

    July 23, 2011 at 8:42 am | Report abuse |
  11. JM

    "What's behind the summer heat?" asks the headline on the main page. Duh, summer???

    July 23, 2011 at 8:59 am | Report abuse |
  12. My2Sense

    Climate change has always, and will always occur.

    Because there are an infinite number of reasons for climate change, the rate and effect of change are difficult to predict.

    People who study climate change believe we are experiencing an unprecedented rate of change, and believe the effects of such an accelerated rated may be catastrophic.

    People who profit from the production, distribution, and sale of petroleum products are attempting to influence public opinion that the source of their income is not the cause of the problem.

    Undoubtedly, both sides have vested interests, but petroleum is the blood of the most profitable companies in the world and their determination to protect it cannot be underestimated.

    Believe what you want,
    choose to think or let your frustration and insecurity make your choice,
    reap what you sow

    July 23, 2011 at 10:37 am | Report abuse |
    • Mobius007

      My2Sense – I agree with your points. This year alone, assuming that the average price of WTI oil remains above $100, over $ 1 Trillion dollars (US) will be transferred to the OPEC nations, through their exports of oil. This dwarfs the past profits of tobacco companies, which in their day had massive propaganda engines that consistently “proved” the safety of tobacco products.

      Unfortunately, these points are mute. There is a growing body of evidence that we have already entered into a positive feedback loop, given the current level of atmospheric CO2, and global warming will continue (even if humanity were to make changes to fossil fuel consumption, which is impossible).

      The world burns MORE oil, coal and nat gas every year. Each year MORE CO2 is released into the atmosphere than the year before. This trend won't change until peak oil is clearly established, and we are forced to lower our reliance on fossil fuels due to their escalating costs. But as I said earlier, even the looming crisis of peak oil won’t change the global warming equation.

      Let's face it – we are already screwed, and future generations will pay dearly for our ignorance.

      Live your remaining days well, knowing that you were one of the fortunate generations to prosper during the century of plentiful fossil fuel.

      July 23, 2011 at 9:14 pm | Report abuse |
  13. Delguy

    It's amazing that the right wing morons on this page would take the word of agenda driven liars over "People who seek truth" I.E. SCIENTISTS. These folks apparently would go to their nearest dry cleaner if they were having a heart attack!

    July 23, 2011 at 11:01 am | Report abuse |
    • Caz

      There are many scientists who say this warmth is part of a natural cycle, too.

      July 23, 2011 at 12:50 pm | Report abuse |
    • My2Sense


      I believe there was a time when "many scientists" made a pretty good living studying the effects of cigarette smoking – funded by the tobacco industry...

      July 23, 2011 at 1:07 pm | Report abuse |
  14. Tom

    It's the SUN, stupid. We are at the mid-point between ice ages, what should we expect?

    July 23, 2011 at 11:17 am | Report abuse |
    • Brian Dodge

      Solar output just passed a minimum, and is only about 15% of the way back to the maximum it had in 2000. Scientists predicted back in the 70's that global warming would lead to higher humidity; higher humidity in the summer creates deadly heat waves; higher humidity in the winter makes for record snowfall. Even if the dice are loaded, the occurrence of an individual roll of snake eyes is random (weather); over the long term, you'll lose more often with loaded dice (climate change – more droughts, floods, record snowfalls, record high temperature, heat waves). The fossil carbon we've burned to increase the atmospheric CO2 from 280 to 390 ppmv has loaded the weather dice, and our losses will continue to mount.

      July 23, 2011 at 11:48 am | Report abuse |
    • Caz

      Agreed. And since the thermometer was invented at the coldest point of the entire holocene, it is not surprising at all that records get broken as the temperature returns to the zenith of the natural, millennial cycle.

      July 23, 2011 at 12:54 pm | Report abuse |
  15. David

    Did anybody consider that it could be both a combination of the earth's natural cycles and the fact that humans have indeed made some changes to our environment that might be contributing to the change. It doesn't have to be black or white (or liberal vs. conservative, or republican vs. democrat, etc.).

    July 23, 2011 at 12:20 pm | Report abuse |
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