Relative Humidity: A Key Weather Variable — Passage and Quiz

Relative humidity is a measure of how much water vapor is in the air compared to the maximum amount the air can hold at a given temperature. It is expressed as a percentage. For example, if the relative humidity is 50%, the air contains half the water vapor it could hold at that temperature.

Relative humidity depends on both the amount of water vapor in the air and the air temperature. Warm air can hold more water vapor than cold air. When air cools, its relative humidity increases, even if the amount of water vapor stays the same. This is why dew forms on cool mornings.

Relative humidity is measured using a hygrometer. It is an important factor in weather forecasting because it affects cloud formation, precipitation, and how comfortable we feel. High relative humidity can make the air feel muggy, while low relative humidity can make it feel dry.

Relative humidity also plays a role in health and safety. High levels can promote mold growth, while low levels can cause dry skin and respiratory problems.

Fun fact: Relative humidity can reach 100% during foggy conditions, meaning the air is fully saturated with water vapor.