• What is Relative Humidity?
• What is Dew point?
• What is the Wetbulb Temperature?

What is Relative Humidity?

According to our Glossary, "Relative Humidity is the ratio of the existing amount of water vapor in the air at a given temperature to the maximum amount that could exist at that temperature. It is usually expressed in Percent." The problem with Relative Humidity is that it changes with the temperature so it's hard to compare versus time. In other words, assuming the temperature is cold at night and hot during the day, the humidity will always be higher at night and lower during the day. The measurement that meterologists prefer is called Dew point. See below.

What is the Dew point?

According to our Glossary, the dew point is "the temperature to which a sample of air must be cooled, while the mixing ratio and barometric pressure remain constant, in order to attain saturation by water vapor. When this temperature is below O°C, it is sometimes called the frost point." In simpler terms, it is a measure of how moist the air is. Moist air is more unstable, which is why you hear meteorologists talking about the Dew point when they talk about thunderstorms. Dew points in the 50's and higher can significantly contribute to thunderstorm development, and Dew points in the 70's indicate extremely unstable air. Since it not expressed as a percentage related to temperature, it won't change day to night like the Relative Humidity (see above).

What is the Wetbulb Temperature?

According to our Glossary, the Wetbulb Temperature is "the lowest temperature that can be obtained on a wet-bulb thermometer in any given sample of air. Obtained by evaporation of water (or ice) from the muslin wick. Used in computing dew point and relative humidity."