Humidity and Dew Point
Some people describe humid weather as muggy. The maximum amount of vapor that can be in the air depends on the air temperature. Warmer air can hold more water vapor within it. That’s why the muggiest days usually happen at the height of summer heat. But as the temperature goes down, the air can hold less vapor and some of it turns into liquid water.
What's the Dew Point?
Why are there water droplets on the grass on a cool summer morning, even though it did not rain the night before? The water most likely came from water vapor condensing from the air when it cooled to the dew point. The dew point is the temperature when water will start to condense out of the air.
Your Turn: Calculate Relative Humidity
On a warm 76°F day, you measure that there is half a gram of vapor for each cubic yard of air.
At that temperature, air is able to hold 1 gram of water for each cubic yard of air. So what is the relative humidity?
Divide the amount of vapor in the air (0.5 grams) by the total amount the air can hold (1 gram) and multiply by 100 to figure out relative humidity as a percentage.