How to adjust training for the summer humidity?

Pretty much everything. RH is meaningless. It's the Dew Point that counts.

The Dew Point Temperature - A Better ApproachSteven L. Horstmeyer

The Concept

Humidity is a complicated concept. Humidity refers to evaporated water substance in the air, i.e. water vapor. For years relative humidity has been what we use to inform the TV audience, but it has many pit falls and to tell you the truth almost no one understands it, including many meteorologists.

Think Energy

When thinking of humidity you always have to think in terms of energy. Of course this is expressed as temperature. There is only so much energy to go around and only a certain part of the thermal energy can go to do the work of evaporation. The rest goes to the other molecules in the air.

Relative humidity expresses how much of the available energy has been used. A relative humidity of 50% means half the energy has been used to evaporate water from the ground, streams, lakes anywhere else it is and 50% is still available to do more evaporation.

Relative to What?

On a summer morning the temperature may be 75 degrees and the relative humidity 90%, a very sticky morning indeed. Without changing the amount of water vapor in the air if the temperature hits 92 degrees in the afternoon the relative humidity is 52%. Relative humidity is RELATIVE TO THE AMOUNT OF ENERGY AVAILABLE Because the amount of energy increased as the sun warmed the atmosphere the percentage of the energy used decreased, i.e. the relative humidity, all the while there was no change in the amount of vapor in the air.

So when you hear someone say its feels worse than 52% relative humidity today, they do not understand the concept of RELATIVE HUMIDITY. Ninety-two degrees and 52% is a very humid afternoon. Because the concept is confusing many meteorologists are trying to get use dew point temperature.

The Dew Point Temperature

Dew point temperature is a measure of humidity. If you take a parcel of air, and cool it, eventually you will remove enough energy to begin to get water vapor to condense. Remember the water vapor was originally liquid water and to get it to evaporate you had to add energy. As long as it has sufficient energy it will remain vapor, but as you cool it at some point condensation will occur. The temperature where condensation begins is the dew point temperature. In terms of relative humidity, as the parcel of air is cooled, the relative humidity increases, when the relative humidity reaches 100%, you are at the dew point temperature.

Dew Point vs. R.H.

Unlike relative humidity if dew point increases, it is only because the amount of moisture increases. If relative changes it can be because of temperature change or moisture change, two variables leads to too many possibilities, with dew point it is strictly moisture you are tracking.

Dew point can never be higher than the temperature, at saturation, i.e. 100% relative humidity the temperature and dew point are the same. …

So How Does Dew Point Feel?

On a typical summer day the following apply:

________________________________________

• Dew Point(F)..........Perception

________________________________________

• 75+....................Extremely uncomfortable

• 70-74...................Very humid, quite uncomfortable

• 65-69...................A bit uncomfortable for most people

• 60-64...................Ok for most, but everyone begins to feel the humidity

• 55-59...................Comfortable

• 50-54...................Very comfortable

• less than 49...................Feels like the west, very pleasant, a bit dry to some

A Common Misconception

One last thing if you ever hear someone say it was 90 degrees and the humidity was 90%, that has never happened in Cincinnati, (and unless the greenhouse effect goes into overdrive never will). 90 deg/90% requires a dew point of 85.5 degrees. In Cincinnati the highest ever dew point was 81 deg. for just a few minutes.

In August 1995 we had four hours of 78,79,78,77 degree dew points, the highest persistent dew points I have seen in Cincinnati since working here as a meteorologist. For one hour I did see a dew point of 81, just after a thunderstorm.

World Record Dew Points

However veterans of the Persian Gulf War know what 90/90 feels like. The Persian Gulf and Red Sea both attain sea water temperatures in the mid 90's. That's plenty of energy, along with the 115 degree air temperatures, to evaporate water.

The dew point has been measured on the shore of Ethiopia, the area is now part of Eritrea, at 94 deg. F. The highest known dew point temperature in the world. The relative humidity with a temp of 115 and a dew point of 94 is 54% this doesn't tell you as much as the dew point when you consider the table above.

5.14.2010 DOHA Kipchoge 12:51 Chepkok 12:51 ================================

Again, for the n-teenth time, there is temperature and there is temperature. Temperature is a measurement. Humidity is a measurement. The key measurement of energy in the air is DEW POINT.

The race was run at night. Sunset at near the Equator is 6:00pm. That means the race went off two and a half hours past sunset. There is NO radiant energy coming from the Sun. There is little stored energy in the air. It's a good time to run.

The 5000m went of at 8:35pm. The temperature was about 94, the DEW POINT was 54. In other words it was ideal for running fast. The physiological benefits of a higher entropy without barriers to heat dissipation.

SDSU Aztec wrote:

Kvothe wrote:

For whatever god forsaken reason, its easier to run in the shade at the same temp. I think it might be because official temps are taken in the shade. Meaning 90 in the shade is 90 in the shade, but 90 in the sun is hotter. Even if I'm wrong, we know running a forested path is a lot easier than running down a treeless road in summer.

The sun does not heat up the air so the tempature is the same for both in the shade and not in the shade.

Please stop with this nonsense. This is Meteorology 101.

Here's a few other threads on Letsrun which touched on the running related effects of Dew Point, and the Corn Effect, which figured prominently in the Paul Short XC race a few years ago.

b]World Record Dew Points

However veterans of the Persian Gulf War know what 90/90 feels like. The Persian Gulf and Red Sea both attain sea water temperatures in the mid 90's. That's plenty of energy, along with the 115 degree air temperatures, to evaporate water.

The dew point has been measured on the shore of Ethiopia, the area is now part of Eritrea, at 94 deg. F. The highest known dew point temperature in the world. The relative humidity with a temp of 115 and a dew point of 94 is 54% this doesn't tell you as much as the dew point when you consider the table above.

Highest Dew Points

http://www.wunderground.com/blog/weatherhistorian/record-dew-point-temperatures

Corn and humidity

https://www.citylab.com/environment/2019/07/corn-sweat-summer-humidity-hot-weather-heat-dome/594409/

http://www.weather.com/outlook/weather-news/news/articles/evapotranspiration-corn-belt-humidity_2011-07-13

https://www.google.com/search?q=cornfield+humidity&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

Humidity in the South thread

https://www.letsrun.com/forum/flat_read.php?thread=3985192&page=1

Paul Short Lehigh humidity

https://www.letsrun.com/forum/flat_read.php?thread=5427811&page=1

readerrrr wrote:

peterpumpkineater69 wrote:

[quote]Nutsack McGee wrote:

And it is always better to be out of sunlight than in sunlight.

Is there a different "quality" to direct sunlight vs shade? Meaning, will 90 degrees in the shade have the same effect on the body as 90 degrees in direct sunlight? Of course there is a difference in UV ray exposure but the effect on heat or running is something I'm unclear on and can't seem to find an answer to.

Great question. I asked the same question when I first moved to north Mississippi (80 miles south of Memphis) and began training through the summer months.

My anecdotal discovery was that there was a sort of triple witching hour, between 8:30 and 9:30 AM on sunny days, when humidity remained very high, temperature was coming on strong--because the meridional sun is strong (and yes, that IS a word) and quickly raises temps--and, in addition, radiant sun was directly heating your skin and raising your body temperature, rather than indirectly raising it through air temp and the pressure on your cooling system created by high humidity.

If I started a two-hour long run at 6:45 or 7, then by 8:30 or 8:45, in that final couple of miles, I was going to take a serious hit.

Triple witching hour.

I ended up switching my long runs so that the first three miles had me running up to a forested trail, and the last three miles had me running home. The middle 6-8 miles, out and back on that trail, kept me out of direct sun AND, by keeping me in shaded woods, had me running in cooler temperatures.

That was a good strategy.

But your skin and body heat up when irradiated by the sun in a way they don't when you are in the shade.

malmo wrote:

Nutsack McGee wrote:

What was I wrong about?

When am I ever going to go out for a run and know what the RH or dew point are but not know the dry bulb temperature?

Pretty much everything. RH is meaningless. It's the Dew Point that counts.

The whole long-winded post that went along with this doesn't indicate that anything that I stated is wrong, much less that "pretty much everything" that I said was wrong.

You merely present your opinion that you would prefer to know the dew point rather than RH if you could only know one. I see the merit in the opinion that you could know only the dew point and estimate thermal comfort. My main point was that I like to know relative humidity because it tells me how far from equilibrium the concentration of water in air is and the potential for evaporation of sweat in a very intuitive manner (0-100 scale). If you were not allowed to know the dry bulb temperature, then I, like you would choose to be told the dew point rather than RH. However, the other part of my argument was that I cannot imagine that I will ever be in a situation where I do not know the dry bulb temperature but I do know either RH or dew point.

I'll give you the benefit of the doubt that you were trying to dumb down your post intentionally, but it reads like meteorologists have a far too simplistic understanding of thermodynamics and heat transfer.

Just quit while you are miles behind. Everything you have claimed in this thread shows a complete lack of understanding of psychrometrics. Malmo's post is 100% on point.

I'm in love with summer but when I don't like the humidity on this holiday. I have had a lot of problems with my basement during the summer. When it was raining the air there was really wet. This was a big problem. Now I found on the internet this https://aerostate.org/best-dehumidifier-for-basement blog about dehumidifiers. There I read that we have on the market a lot of dehumidifiers but we have to choose the one that will fitty us and our necessity. So this is how I got prepared for the next summer. Can't wait to try it.