What does "dew point" mean? Dew forms when a surface, such as a leaf or a car hood, cools to the dew point of the air with which it comes into contact. If the dew point temperature is above freezing, water vapor in the air condenses onto the surface in the form of dew. If the dewpoint is below freezing, the result is frost. Warmer air has more capacity for water vapor, so cool nights following warm days (typical of late spring and early fall) promote dew formation.
What is "relative humidity"? Relative humidity is a ratio of how much water vapor is in a given volume of air compared with the amount of water vapor that would saturate the air at a given temperature and pressure. Because it’s a ratio, relative humidity is given as a percentage. When the air is saturated and contains the maximum amount of water vapor, the relative humidity is 100%. For a given amount of water vapor in the air, relative humidity will decrease as air temperature increases and increase as air temperature decreases.
Absolute humidity is the total amount of water in a given volume of air.