Say you have a given amount of water vapor in the air. Relative humidity as a percentage reflects the amount of water vapor in the air compared with the maximum

Say you have a given amount of water vapor in the air. Relative humidity as a percentage reflects the amount of water vapor in the air compared with the maximum amount of water vapor the air could hold at that temperature (and pressure). The amount of water vapor the air can hold depends on the temperature, with higher temperatures able to carry more water vapor. As the temperature goes down, the amount of water vapor stays the same while the amount the air can carry decreases, so the relative humidity goes up. https://en.wikipedia.org/wiki/Relative_humidity https://en.wikipedia.org/wiki/Relative_humidity