I was reading an article on Japan’s weather for the Olympic being so hot and the author said “with a dew point of 72 degrees what do you expect?”.
I don’t know what to expect!
In: Chemistry
Air can only hold so much water. At 100% humidity, that is the point it cannot hold any more. So, the higher the humidity, the less sweating/being wet can cool you down. The hotter the air, the more water it can hold
The dew point is the temperature at which water will condense out of the air. The actual equations are complex, but in day to day life, it is a measure of how hot it *feels*. The higher the dew point, the hotter it feels, and the harder it is to cool down. Anything about 65F generally feels uncomfortable
The dew point is one way of measuring the absolute amount of moisture in the air.
The amount of moisture than air *can* hold is greatly dependent on temperature. At 50 F, air can have up to 1.21% water vapor. At 68 F, air can have up to 2.31% water vapor. At 77 F, air can hold up to 3.13% water vapor.
So, if you take the percent of water vapor in the air and then map it to the temperature where that amount is the maximum (or “saturated”). It is called the dew point because when when the temperature of the air is the same as its dew point, then air is “full” of water and dew will often form on the grass.
Two things about dew points. First, higher dewpoints simply means air with more moisture in it. Second, when the dewpoint and the temperature are close, then the *relative* humidity is high. That means that dew might form, fog might form, sweat will have trouble evaporating. So a dewpoint of 40 F means different things when the temperature is 40 F (a cold misty day) or when the temperature is 90 F (dry day because the air is .8% water when it *could* have 4.8% water) even though it is the same *absolute* amount of water in the air.
This stuff is complicated. Let it sink in for a while.
Dew point represents the air’s ability to retain water. Basically it’s humidity. It’s the temperature at which water will start to form dew on surfaces because the air won’t be able to hold any more moisture.
If you have a dewpoint of 78, that means that there is 100 % humidity up to 78 degrees. (25.5 Celsius) that’s going to be an extremely hot and incredibly muggy and humid air to operate in.
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