Talk:Dew point/Archive 1

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Archive 1

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What are the dew point comfort ranges? Why do we have dew pointss? — Preceding unsigned comment added by 72.152.218.24 (talk) 21:11, 12 March 2012 (UTC)

Calculating dew points?

What is a good empirical formula for calculating dew points based on temperature and relative humidity?

See the third and fourth external links. I wrote a little program that caluclated the dew point and heat index, and I used the third one. Bubba73 23:09, July 19, 2005 (UTC)

I added the formula to the article. Bubba73 02:41 and Wind Chill can be downloaded. Bubba73 03:08, August 1, 2005 (UTC)

Formula seems inaccurate

I used this formula vs. wunderground.com's ambient conditions, and the formula was incorrect. -- 130.18.64.104

The formula matches one in a book I have, perhaps the wunderground algorithm is wrong? furthermore, if I let Tdp = T I get RH = 1 which makes sense. Can you give more precise examples where it fails? njh 23:15, 14 February 2006 (UTC)

For the formula to work, RH needs to be in the range 0 - 1 not a percentage —Preceding unsigned comment added by 78.32.26.49 (talk) 16:08, 29 June 2009 (UTC)

Dew Point what?

This article needs to be re-named. Dew point is ambiguous. There are two phycial properties that are closely related Dew Point Pressure AND Dew Point Temperature. The article clearly is speaking of the latter.

When one says "the dew point" it is often correct to assume that the dew point temperature is being spoken of, however, this is not always the case.

In addition the dew point temperature of a gas or vapor is dependent on the absolute pressure of the gas - that is to say: dew point temperatures must always be refrenced to a pressure and dew point pressures must always be referenced to a temperature.

The article doesn't explain or ellude to this important relationship.

This "dew point pressure" you mention goes by another, more common, name: saturation vapour pressure. mdf 19:09, 17 July 2006 (UTC)

Dew point calculators

Figure 1

This figure looks like it was done in about 1 minute with very little effort, should this figure not be polished up significantly? chiefhoser 08-08-2006

Question

how can the dew points be changed? Can dew points only be changed by temperature?

Wikipedia:What_Wikipedia_is_not

Talk pages are not mere general discussion pages about the subject of the article, nor are they a helpdesk for obtaining instructions or technical assistance. If you wish to ask a specific question on a topic, Wikipedia has a Reference desk, and questions should be asked there rather than on talk pages.

-Ac44ck (talk) 02:18, 14 March 2012 (UTC)

remark

the article defines very nicely what dewpoint temperature is and how it can be calculated. What i'm missing here is some background information on what determines the dewpoint. (Relative humidity, yes, but what influences RH? You can't just say RH is determined by DP, and DP is determined by RH, you have to give information on what influences the relative humdity/DP which should be considered as one factor, since RH is just the consequence of the DP and T)

Dew point and temperature

I'm confused. The article says that "If the temperature rises without changing the absolute humidity, the dew point will rise accordingly." Since the absolute humidity is "the mass of water in a particular volume of air" and the dew point temperature is "the temperature to which the parcel must be cooled, at constant barometric pressure, for water vapor to condense into water", it seems to me that for a fixed, isolated parcel of air, the dew point temperature is independent of the current temperature of this parcel.

So I do not understand why the dew point should rise? —Preceding unsigned comment added by Ph martin (talk • contribs) 27 June 2007

I got tangled up in that one too. I think the writer meant to say "If the PRESSURE rises without...." Earlkio (talk) 22:40, 2 July 2010 (UTC)

Temperature Range on Dew Point Formula?

I think that range 0 < T < 60 is only due to the sensors on the reference page equipment... the RTD temp sensor device. Otherwise, I think that derivation and formula should be valid up until 100C? I have changed this on the page. Does anyone know better? --Phatmattbaker 16:31, 30 August 2006 (UTC)

High RH

In Melbourne today - Saturday January 20th 2007 at 8:00 pm the RH is 88 and the dew point is 20.9C (figures from the University of Melbourne's weather site at http://www.earthsci.unimelb.edu.au/weather_page.htm )

203.222.159.54 09:12, 20 January 2007 (UTC)

Record Dewpoint

Anyone know the highest dew point ever recorded? I haven't seen anything above 86F.

Answer from mtn-man... The record high dew point in the world is 93 degrees, observed near Dubai, on the Persian Gulf in the United Arab Emirates. 22:20, 31 January 2007 (UTC)

Comment on 24 October 2007 ... mtn-man answer of 93°F near Dubai, UAR is often suggested as the world record highest dewpoint temperature; however the date of 31 January 2007 is suspect because the weather records for that date at Dubai International Airport and at Sharjah International Airport indicate a maximum recorded dewpoint on that date of 16.8°C (62.2°F). In US Air Force report AFCRL-70-0563 dated 6 October 1970 Grantham and Sissenwine of the Air Force Research Laboratories reported a 33.6°C (92.5°F) record dewpoint for Sharjah in the month of July. The year of this event in vague and some evidence suggests that it was in the period 1940-1953. One problem in determining the record high dewpoint is that most world meteorological stations record temperatures every three hours in contrast to some who claim a high dewpoint record only list a single instantaneous reading often not at an official meteorological station. Many claims for record dewpoints originate at desert locations when an approaching thunderstorm thrusts a short duration burst of moisture into a location.K289g 15:14, 24 October 2007 (UTC)

I cannot find any verification for the unsubstantiated claims for record dew points:
http://www.wunderground.com/history/airport/OEDF/2003/7/8/DailyHistory.html
http://www.wunderground.com/history/airport/OMDB/2007/1/31/DailyHistory.html
Therefore, I removed the text in the article.
--Baden187.132.3.243 (talk) 09:30, 27 March 2010 (UTC)

usefulness

55 comfortable
60 sticky
65 muggy
70 oppressive
75 unbelievable
80 I saw only once here.
source: Todd Gross WHDH-TV NBC Boston Channel 7

it looks like this chart explains why the dew point is useful. who really cares what the dew point is unless it can give you useful immediate information. shouldn't this be added to the article? Kingturtle 03:28, 17 September 2006 (UTC)

The Houston Chronicle has a good article about the uselessness of dew point at http://www.chron.com/disp/story.mpl/headline/features/4100421.html Ewlyahoocom 18:58, 18 February 2007 (UTC)

Dew point and absolute humidity

The beginning of the article says that dew point is the temperature to which humid air must be cooled, while maintaining the same pressure, to cause its water vapor to begin to condense: i.e., the saturation temperature of the water in the air at whatever the partial pressure of water vapor is. This matches up with what I remember from thermodynamics. If the temperature is increased while maintaining the same absolute humidity (mass of water per volume of air), the partial pressure of water vapor has been increased (although water vapor close to saturation is not an ideal gas by any means, it still exhibits the same trends, so if mass and volume are held constant while temperature increases, pressure must increase). This, in turn, means that the saturation temperature must increase (the mixture of water vapor and dry air now does not need to be cooled as much to cause the water vapor to start condensing).

   Dbrunner 01:11, 12 July 2007 (UTC)

Dew point, Real Feel Temperature, Heat index, Wind chill, Humidity

What are the differences and similarities of the calculations?... for (a) Dew Point?... (b) Real Feel Temperature?... (c) Heat Index?... (d) Wind Chill?... (e) Humidity?... [e-mail] 11:43, 22 July 2007 (UTC)

The "calculations" aren't really similar, as they are all measures of different things, excepting that dew point is one measure of humidity. See the articles on humidity, heat index and wind chill. "Real Feel" is a made up thing from Accuweather. --skew-t 09:15, 12 October 2007 (UTC)

Pictures of dew?

The photos "Dew on a spider web", "Dew On Webs" and "Dew On plants" are appropriate for the article about dew, but don't contribute anything to the understanding of dew point. They should be deleted. Opinions? dwboston 05:59, 29 July 2007 (UTC)

Agreed; I thought the same thing when I saw them. --skew-t 09:17, 12 October 2007 (UTC)

Celsius

What's with the Fahrenheit? Someone should replace the F:s with C:s - I don't trust my knowledge of F/C conversion enough nor do I have any celsius sources to do it by myself. As the article now stands it's practically unreadable to an international reader. - G3, 14:05, 3 September 2007 (UTC)

I looked at changing the units myself, but I stopped as although farenheight is unknown to me, what unit was the original measurements in?

Answer

To convert Farenheit to SI, divide by 1.8 and add 255.38. For example 70 Farenheit is 70/1.8 +255.4 294.3 K. 71.175.155.251 (talk) 14:43, 4 September 2009 (UTC)

Why Only for Air-Water Mixtures&nbsp;?

This article assumes that the term dew point applies only to air-water mixtures when it can apply to any mixture of two or more components. When cooling a mixture at constant pressure the dew point is the point that the first drop of liquid forms. Similarly when heating a liquid, the bubble point is the temperature that the first bubble is formed. Event Horizon 23:40, 16 September 2007 (UTC)

How about providing some references to papers or texts that use the term dewpoint for condensible mixtures not involving water? If this is a common usage, then a short note extending the article to non-aqueous mixtures would certainly seem appropriate to me.Easchiff 15:59, 17 September 2007 (UTC)

The term is used extensively in the Chemical Engineering field. Any text on Mass Transfer or distillation will refer to the bubble point and dew point of the mixture being distilled. The classical text is "Mass Transfer Operations by Trebal" I do not have access to a copy unfortunately. Maybe someone else can help out. Event Horizon 23:36, 17 September 2007 (UTC)

I'll try to get hold of R.E. Treybal's book, or something equivalent.Easchiff 14:54, 19 September 2007 (UTC)

Here are two references:

Gatley, D., Understanding Psychrometrics, ASHRAE (2003), pages xi and 269

Treybal, R., Mass-Transfer Operations. 3rd Edition, McGraw-Hill (1981, page 229

Quote. Some broaden the definition of psychrometrics to cover mixtues of the gas of one substance (any dry gas component or a mixture of dry gases) and the condensable vapour of a second substance. Examples include hydrogen-water, hydrogen-carbon tetrachloride, oxygen-carbon tetrachloride, air-toluene, air-bezene.

The book "Handbook of Psychrometric Charts, D.C. Shallcross, Kluwer (1997) contains over 300 charts of which 38 apply to air-water vapour and the remainder are other hydrocarbons and other chemical substances.

Since the Wikipedia "Psychrometrics" section begins with "Psychrometrics or psychrometry are terms used to describe the field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures." this should be sufficient justification to change the wording in dew point {temperature}. k289gK289g 16:15, 4 November 2007 (UTC) K289g 13:48, 5 November 2007 (UTC)

WikiProject class rating of Start

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:48, 10 November 2007 (UTC)

If no inline references are added to this article, it will remain start class, and therefore will be less likely to be used within wikipedia by users. Wikipedia users are getting more savvy in checking out the class of articles in order to determine their usefulness. Thegreatdr (talk) 15:29, 6 April 2008 (UTC)

ugly excel graph

Is there no better alternative for this ugly MS Excel graph? --85.146.199.125 (talk) 22:40, 15 January 2008 (UTC)

"Feels like the western US"

That is not much use to the vast majority of the world who've never been to the western US! 86.143.48.55 (talk) 16:02, 29 January 2008 (UTC)

Denver and New York?

From the 'Constant pressure' para:

"For this reason, the same dew point in New York and Denver (which is at a much higher altitude) will imply that a higher fraction of the air in Denver consists of water vapor than in New York."

From the 'Varying pressure' para:

"Coming back to the New York - Denver example, this means that if the dew point and temperature in both cities are the same, then the mass of water vapor per cubic meter of air will also be the same in those cities."

How can these both be true? —Preceding unsigned comment added by 82.70.243.134 (talk) 09:37, 5 February 2008 (UTC)

Consider a box of air at Denver, and a box of air in New York.

Even though Denver's box is just as big as New York's box, it holds less air -- there are fewer total molecules in Denver's box.

(When the temperature is the same, I estimate that Denver's box has roughly 0.8 times as many molecules as New York's box).

However, when the dew point and the temperature in both cities are the same, then both boxes hold the same number of water molecules.

Since both boxes have the same number of water molecules, but Denver's box has fewer other air molecules, the ratio of water molecules to total air molecules in Denver is higher.

How could we change the article to make this easier to understand?

--68.0.124.33 (talk) 15:06, 31 October 2008 (UTC)

The whole premise of the "Varying pressure" section is a little odd. One shouldn't have to hold temperature constant in order for dew point to indicate absolute humidity. You can raise and lower the temperature and pressure all you want; it's not going to change the mass of water vapor in the air, and it's not going to change the temperature at which that water vapor condenses. In fact, dew point is merely one way of expressing the absolute humidity, so it's going to be an indicator of absolute humidity no matter what the air conditions. It would be fair to say that fixing the temperature and allowing the air pressure to vary makes dew point into an indicator of partial pressure of the water vapor. However, the paragraph under "Explanation" already does a really excellent job of explaining the relationship between partial pressure and dew point, so it would be a shame to have turn this confusing paragraph into a poor attempt to re-explain what has already been explained well. I suggest relabeling the "varying pressure" section into "relation to absolute humidity", and rewording it to indicate that dew point is just a different way of expressing absolute humidity. Then the New York / Denver sentence could remain unaltered. To be parallel, I would also suggest renaming the "constant pressure" section into "relation to specific humidity", although that paragraph itself doesn't have to be reworded. I'd do it myself but I want to double check that I'm right about this first. Riick (talk) 07:51, 16 January 2009 (UTC)

Graph

Just as a matter of clarity, it would be nice if the first sentence under Explanation was caption under the graph. (Or, some other caption that explains it without the need for the user to read the article to find out what the picture represents.) This is mainly a convenience issue for the user I guess and if I had the time or familiarity with wikipedia source code to do it, I would, but I have to start heading to class soon. Thanks. Parryield (talk) 12:38, 9 March 2009 (UTC)

Measuring dew point

I thought the wikipedia entry for dew point has an inadequate definition. Especially for persons like me who see the dew point listed on a weather report and want to know exactly what it means. Only after spending a lot of time reading everything written about dew point in wikipedia and the supplied links have I finally been able to surmise that dew point is not a reading ..... but a calculated value. That should be the first point made in the definition if I have gotten that idea correct. Since it is a calculated value, and not an actual reading, doesn't that also imply it will have no effect on plants, such as those that are tender to frost? Thus if a temperature reading is 33 F and the dew point is 27, isn't it so that there should be no frost damage to plants that can tolerate temperatures down to actual freezing which is 32? The definition should cover all this, or it is worthless to someone like me. 68.43.123.159 (talk) 11:12, 18 May 2009 (UTC) Mike Price

Dew point is measurable, or perhaps better, observable -- it need not be calculated. A chilled mirror hygrometer can be used to measure (or make evident) the dew point. A description of the principle of operation of this instrument begins on page 3 of this document:

http://www.gesensing.com/downloads/manuals/E4-1111H-GE.pdf

If the dew point is 27°F, "dew" will be in the form of frost and the plant may freeze. The air temperature cannot be lower than the dew point. If the dew point is 35°F, condensation will be in the form of liquid water, the air temperature is at least 35°F, and the plant will not freeze. - Ac44ck (talk) 00:38, 19 May 2009 (UTC)

Specific to the original question, a dewpoint below freezing is in no way a threat to tender plants. The dewpoint is a measure of air humidity although it is expressed in degrees. For the care of plants you should look at the forecast minimum temperature, but also be aware that this is the air temperature at some distance from the ground. Freezing conditions at ground level and frost can occur when the official air temperature is several degrees above freezing. If you want to get more advanced, you can start to form your own predictions by looking at the dewpoint. When the air temperature drops close to the dewpoint, water starts to condense out and this releases a considerable amount of heat. Mist or low cloud may also form, again limiting the drop in night temperatures. When the dewpoint is very low, the air can cool much more quickly with no checks, and this is one reason that nights are cold in the desert. Watch out for very cold conditions where the dewpoint may drop rapidly at night as the small amount of air moisture quickly freezes out. —Preceding unsigned comment added by 90.206.27.152 (talk) 15:50, 4 February 2010 (UTC)

Constant and Varying Pressure?

I suspect the respective discussions are reversed. (--Wesgin (talk) 17:13, 4 October 2009 (UTC))

This appears to be your first edit on Wikipedia. There is don't bite the newcomers. Please note the construction of the talk page. There is a 'new section' button in the tabs at the top of the page.

It appears that the 'new section' button wasn't used because the new comment was top-posted. It took some detecitve work to figure out what was added to the talk page.

Whether to top- or bottom-post is a religious issue, but the convention on Wikipedia (evidenced by the behavior of the 'new section' button) is to bottom-post.

And please elaborate. The comment is too terse. Why is there the suspicion that the discussions are reversed?

-Ac44ck (talk) 20:27, 4 October 2009 (UTC)

Dew Point less than the freezing point of water

The first graph implies that the dew point can be less than the freezing point of water (close to -60C). The second implies that it can't be. Which is true? If the first is true, how can water exist in a gaseous state at sub-freezing temperatures? —Preceding unsigned comment added by 86.155.155.209 (talk) 17:21, 7 March 2010 (UTC)

Table obviously incorrect in column "Rel. Humidity at 32 °C (90 °F)"

The table has strange values in the right-hand column - some ranges are non-contiguous, others overlap:

Dew Point °C	Dew Point °F	Human Perception[1]	Rel. Humidity at 32 °C (90 °F)
>Higher than 26 °C	>Higher than 80 °F	Severely high. Even deadly for asthma related illnesses	65% and higher
24 - 26 °C	75 - 80 °F	Extremely uncomfortable, fairly oppressive	62% <-- should be a range here
21 - 24 °C	70 - 74 °F	Very humid, quite uncomfortable	52% - 60%
18 - 21 °C	65 - 69 °F	Somewhat uncomfortable for most people at upper edge	44% - 52%
16 - 18 °C	60 - 64 °F	OK for most, but all perceive the humidity at upper edge	37% - 46% <-- overlaps row above
13 - 16 °C	55 - 59 °F	Comfortable	31% - 41% <-- overlaps row above
10 - 12 °C	50 - 54 °F	Very comfortable	31% - 37% <-- two ranges start at 31% ???
<10 °C	<49 °F	A bit dry for some	30%

I wrote a C++ app (for my own purposes). I notice that my own (Fahrenheit) calculations, using the first formula (August-Roche-Magnus approximation), have different values for the humidity:

>80 °F	Severely high. Even deadly for asthma related illnesses	72% and higher
75 - 80 °F	Extremely uncomfortable, fairly oppressive	61% - 71%
70 - 74 °F	Very humid, quite uncomfortable	52% - 60%
65 - 69 °F	Somewhat uncomfortable for most people at upper edge	44% - 51%
60 - 64 °F	OK for most, but all perceive the humidity at upper edge	37% - 43%
55 - 59 °F	Comfortable	31% - 36%
50 - 54 °F	Very comfortable	26% - 30%
<49 °F	A bit dry for some	25% and lower

Can anyone defend the original values?

Unrelated to the numerical problems with the table, the table itself seems really really subjective. I'm amused that the tables suggest that a dew point of 75-80 F is extremely uncomfortable and oppressive... when I live perfectly comfortably in such an environment (dew point 27 C, RH 84 % for today) everyday. --Rifleman 82 (talk) 01:29, 22 June 2010 (UTC)

References

Calculating the dew point

Is the first calculation method in fact a method for determining the wet bulb temperature? This is what I found when I applied it with known values for dry bulb, wet bulb, dew point and relative humidity (within given ranges). —Preceding unsigned comment added by AndyBairstow (talk • contribs) 20:17, 10 August 2010 (UTC)

Wording of first sentence

The grammar used in the first sentence doesn't make sense:

"The dew point is the temperature at which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to condense into water."

Should it not read:

"The dew point is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to condense into water." ?

--Tonylemesmerd (talk) 09:22, 9 December 2010 (UTC)

Small copyedits don't need debate - just make them. Glrx (talk) 16:08, 9 December 2010 (UTC)

Calculating the 'old' way

Query: why isn't the determination of the dew point as a factor in finding humidity explained in "old farmer's terms"? My city's weather station admits to using this as much more reliable for our area than algorithms or exponentials:

1. They literally open the window and stick out a glass of room-temp water with a thermometer in it.

2. The moment the glass begins to develop condensation, it is brought inside and the temp is noted. That is registered as the dew point.

3. The percentage of the temperature that the dew point represents is what is reported as the humidity percentage.

...and I think they screw that up often. Yesterday it was 64, the dew point was 61 and somehow they calculated the humidity at 91% which is clearly wrong. I'm no mathematician but that seems to represent closer to 97%, meaning in my fevered brain I see 61 as being around 97% of 64.

Does anyone else know of what I speak, and agree it should be in the calculating section? Also, why is this exclusively in Celsius? Fahrenheit equivalents ought to be in there.75.21.97.145 (talk) 22:34, 23 June 2011 (UTC)

The "old" way is not accurate. It should not be in the calculating section. Try your given values in the calculator here:

http://www.sugartech.co.za/psychro/index.php

The reported value of 91% is reasonable, allowing for rounding errors. - Ac44ck (talk) 02:45, 25 June 2011 (UTC)

Steps 1-2 don't seem possible with the example given. Let's say room temperature is 68F. The glass of water will slowly cool from 68F to asymptotically approach 64F. With dew point at 61F, condensation will never occur. I guess it would be possible to start with a glass of cold water and see when the condensation on the glass evaporates, but I would imagine there would be a big lag between the time at which the glass's surface reaches the dew point, and the later time (and higher temperature) at which all the condensed water on the glass has evaporated back into the air.

Step 3 is just wrong. Fahrenheit and Celsius temperatures are defined in relation to an arbitrary zero. So calculating a ratio of two temperatures in these systems has no meaning and can't be interpreted as a relative humidity percentage. Sure, if the dew point is equal to the actual temperature, then relative humidity is 100%, but a dew point of 51F with an actual temperature of 68F does not imply a relative humidity of 75% (actually, it would be around 50%). 99.122.55.211 (talk) 21:37, 20 July 2011 (UTC)

Dew point or dewpoint?

One or two words? I'm flipping through a couple of books and they use dewpoint (one word). Is there a consensus for how it should be spelled? 70.129.177.19 (talk) 18:30, 5 July 2011 (UTC)

Trivial Statement?

"The air that affects comfort is not the air where the thermometer and humidity meters are located. It is the air that is touching one's body."

Is it really necessary to state this? It seems unbelievably obvious. — Preceding unsigned comment added by 129.176.151.28 (talk) 15:30, 2 July 2012 (UTC)

Dew point can be negative

Hello, dew point can be negative using the Celsius scale, but also when using the Fahrenheit scale. It's more common that the dew point drops below zero when using the former, but quite rare when using the latter. See the dew point map of Antarctica: http://www.wunderground.com/global/Region/AN/2xDewpoint.html and weather forecast for Antarctica: http://www.timeanddate.com/weather/antarctica/south-pole --Hartz (talk) 16:41, 17 October 2012 (UTC)

Poorly Written?

This article appears a case of many cooks spoiling the broth. I gave up and went elsewhere for the info where I found well written simple introductions which then went into detail. Desperately needs a straight forward and concise introduction no more than a sentence or two. No problem with the denser stuff later but the intro is written by committee to the point of not saying anything. Someone with no prior knowledge of weather would struggle. — Preceding unsigned comment added by Gingerzilla (talk • contribs) 18:45, 20 April 2013‎

Amen to that. This is becoming more typical of Wikipedia articles. Instead of re-writing a sentence with clarity, a new "contributor" will just add "however, this can also ..." or add "Put another way, blah blah". The sentences get longer and more confusing. Same with sections. The article grows longer and more confusing. Surely, there must be a simple formula for calculating dew point. I think I remember one from flight school. Pilots use dew point (temp) to avoid icing conditions. In any case, I had to go elsewhere to find the answer, and this is happening more frequently. Wikipedia's value continues to diminish. — Preceding unsigned comment added by 98.194.39.86 (talk • contribs) 05:03, 5 January 2016

Arden Buck accuracy

As far as I can tell, the 0.05% and 0.06% accuracies given by Arden Buck were only for the vapor pressure, Ps; that's not the accuracy of the dew point calculation. The 'a' factors should be in units of millibar or hPa. — Preceding unsigned comment added by 99.229.75.89 (talk) 02:51, 31 May 2013 (UTC)

added millibar to a coefficients. Glrx (talk) 15:25, 1 June 2013 (UTC)

Makes no sense

"At a given temperature but independent of barometric pressure, the dew point is a consequence of the absolute humidity, the mass of water per unit volume of air. If both the temperature and pressure rise, however, the dew point will increase and the relative humidity will decrease accordingly. Reducing the absolute humidity without changing other variables will bring the dew point back down to its initial value. In the same way, increasing the absolute humidity after a temperature drop brings the dew point back down to its initial level. If the temperature rises in conditions of constant pressure, then the dew point will remain constant but the relative humidity will drop. For this reason, a constant relative humidity (%) with different temperatures implies that when it's hotter, a higher fraction of the air is water vapor than when it's cooler."

This entire paragraph and the following one are awful. They are the long-winded talk of a person who is explaining it to himself for practice by going through cases. But it's not even correct:

"At a given temperature but independent of barometric pressure, the dew point is a consequence of the absolute humidity..."

"If both the temperature and the pressure rise, the dew point will increase..."

The dew point of a sample of air does not depend on the temperature. It is a temperature !!! It depends on the water content of the air and the pressure.

Even the correct parts of these paragraphs are wordy and confusing. These two paragraphs should be replaced by something brief and correct. 84.227.241.146 (talk) 07:24, 13 September 2014 (UTC)

I had exactly the same reaction, as did #10 above, years and years ago. I've added a "confusing" tag in the hope that some good person who knows about dew points comes along and fixes it. 212.44.19.62 (talk) 11:53, 4 March 2015 (UTC)

Frost point???

First of all, this is an article about the dew point, so I don't think it should have a whole section dedicated to the frost point. A "See also" would suffice.

Secondly, the section is obviously wrong in saying that the frost point is always higher than the dew point. If that was true, then on an ordinarily humid summer day, with temperature, say, 25 degrees Celsius, we should see frost on our beer glasses before they are covered in dew. Since, as everyone knows that such a miracle never happens, it's obvious that the dew point must be higher than the frost point.

And finally, the external source referenced (http://www.theweatherprediction.com/habyhints/347/) looks rather flakey to me.

May I suggest that the section be deleted? 83.251.176.228 (talk) 06:14, 24 September 2014 (UTC)

New Edits to Opening Section

In response to the "please help us clarify this article" request, I have added simpler definitions and explanations, citing the national Weather Service glossary and a "Capital Weather Gang" posting from The Washington Post. — Preceding unsigned comment added by Maddencb (talk • contribs) 13:07, 11 July 2015 (UTC)

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Cleanup. Bad translation of recommended humidity data, discomfort happens way over -20 deg dew point - all degs Fahrenheit here

The article states that cracked skin etc can be expected when the dew point is way below zero; however, this can happen at dew points that are as high as the 20s in many people.

Also this:

Discomfort also exists when the dew point is low (below around −30 °C (−22 °F)). The drier air can cause skin to crack and become irritated more easily. It will also dry out the respiratory paths. The U.S. Occupational Safety and Health Administration recommends indoor air be maintained at 20 to 24.5 °C (68.0 to 76.1 °F) with a 20-60% relative humidity (a dew point of −4.5 to 15.5 °C (23.9 to 59.9 °F)).[8]

recommends indoor air be maintained at 20 to 24.5 °C (68.0 to 76.1 °F) with a 20-60% relative humidity (a dew point of −4.5 to 15.5 °C (23.9 to 59.9 °F)).[8]

That is a huge recommended range. I believe what it's meant to be is an inverse sliding range. So up to 60% relative humidity at 68 degrees (53 degree dew point), and as low as 20% humidity at 76 degrees (32 degree dew point). Even that is a huge range, and 32 is about the lowest the dew point can be without pronounced dry air effects such as dry skin, eyes, and bloody noses, etc. And the calculation of a 60 degree dew point at 76 degrees is almost a subtropical outdoor summer amount of humidity. Also consider that more humidity can to some degree make up for cooler air, so a 60 degree dew point at about 70-72 degrees is more comfortable than 60DP/60% humidity at 76 degrees. 20% humidity is very low for the entire range of room temps given, let alone 20% at 68 degrees, which is a 26 deg dew point. Also a factor is that a humidity level above the minimum for comfort may be needed indoors in the cold or winter months to make up for arctic dew points and wind exposure outdoors. The whole article isn't up to good par, and has the tags to show. I may get into fixing this myself and adding some more research and sources. B137 (talk) 18:56, 4 November 2016 (UTC)

Singapore dew point 26 degrees C during summer, but people don't find it SO BAD as this article would suggest

This page states that 26 degrees C dewpoint is extremely oppressive "Severely high. Even deadly for asthma related illnesses" and Numbeo used that to suggest that Singapore has to bad climate: https://www.numbeo.com/climate/in/Singapore But people don't find it so extremely unplesant: https://www.quora.com/unanswered/Does-most-people-find-climate-in-Singapore-unpleasant I need opinions how to fix Numbeo's formula (or this article): https://www.numbeo.com/climate/indices_explained.jsp — Preceding unsigned comment added by Mladen.adamovic (talk • contribs) 18:09, 1 June 2017 (UTC)

WHy use dew point at all?

I would think that 99.9% of the time that anyone is concerned about water content in ambient air they want to know "Will it be hot and humid, or will it be hot and dry?". How many people need to ask what the humidity will be on a comfortable day or even a cold day? So who gives a hoot about "dew" when it is hot? Who is thinking about dew and not about HUMIDITY?

So my point is that there should be a brief explanation of why DP is a better metric in a weather forecast or condition because I notice that all of our weather people forecast in DP values and I really doubt that many people understand or care about this. 76.168.51.241 (talk) 17:56, 10 August 2017 (UTC)

I've removed the indents for readability.

It is too bad that people are that ignorant (as you imply), but it seems the TV weather folks use it ... because it is a defined and measurable feature and quite useful to understand the complexities of weather and forecasting. Vsmith (talk) 20:41, 10 August 2017 (UTC)

 This seems to be the consensus among weather professionals. Can you explain to the lay readers WHY this is so? Can you explain in the article WHY just knowing the humidity value is no longer sufficient to describe a comfort level? I did not see this, maybe I need to read it again. 76.168.51.241 (talk) 16:11, 12 August 2017 (UTC)
 I'm sure this metric has it uses for pilots and scientists and possibly Farmers. Vsmith above says "It is too bad that people are that ignorant...", well yes, we are that ignorant and all ANY lay person,(and non-pilot) is concerned about is the humidity, period. Have you ever heard someone say "It's not the heat, it's the dew point!" Please, get real.  — Preceding unsigned comment added by BrianAlex (talk • contribs) 01:42, 20 November 2023 (UTC)

Are dew points above air temps a thing or not?

"Dew point temperature is never greater than the air temperature because relative humidity cannot exceed 100%."

<--------->

"At temperatures below the dew point, the rate of condensation will be greater than that of evaporation, forming more liquid water."

(Emphases by me.)

How is this not a contradiction? Can somebody explain?

---

74.93.186.81 (talk) 19:44, 9 December 2017 (UTC)

I noticed this and believe it is a contradiction as well. I believe the author might have meant that dew point cannot STABLY be greater than temperature. So if the temperature of humid air suddenly drops below the dew point, water will begin to condense, but there might be a period of time where the water has not finished condensing yet. During that period of time, the dew point is greater than the temperature but the dew point is not stable since water will continue to condense until the dew point equals the temperature. Can anyone confirm if this is correct? If it is, is there a way to calculate how long the condensation process takes at various temperatures and dew points? — Preceding unsigned comment added by 2601:444:C200:F3BF:A1:FCCE:E2C7:9926 (talk) 04:53, 11 January 2018 (UTC)

Calculating the dew point

Is something missing in the explanation? It starts with,

"A well-known approximation used to calculate the dew point, Tdp, given just the actual ("dry bulb") air temperature, T (in degrees Celsius) and relative humidity (in percent), RH, is the Magnus formula: "

... and then mentions "b" and "c" in the formula without explaining what b and c are.

83.25.102.104 (talk) 06:25, 5 September 2018 (UTC)