University of Illinois Extension

Dew Point Temperature

 A graph that show maximum water vapor capacity increasing as temperature increases.

A graph that show maximum water vapor capacity increasing as temperature increases.
Click on the image to view the large version.

If the amount of water vapor in the air stays the same, but the temperature goes down, the relative humidity will increase. This is because the colder air cannot hold as much water vapor.

If the temperature gets cold enough, the air gets to the point that it is holding the most water vapor it can hold. The relative humidity for this temperature would be 100 percent. This is also known as the dew point temperature. Why do you think they call it this? Think of what happens on cool nights. If the temperature gets down to the dew point, some of the water vapor turns back to liquid water – this is called condensation. What do you see in the morning? That dew is just liquid water that has condensed out of the air. It is the same thing that happens when you have a cold glass of something and let it sit for a while – what happens to the outside of the glass?


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