Temperature describes how much heat is in air. Humidity describes how much water vapor is in air. When air temperature changes, humidity relative to that temperature is also apt to change.
Temperature Limits Humidity
The temperature of a parcel of air puts a limit on how much water vapor (humidity) the parcel of air can hold. The warmer the air, the more water vapor it can hold. By the same token, cold air can hold significantly less water vapor than warm air.
Humidity Responds To Temperature
Humidity is water vapor contained in air. At higher temperatures, air can hold more water vapor than the same amount of air at lower temperatures. For example, if a sealed parcel of air experiences a rise in temperature with no addition of water vapor, the relative humidity of the parcel of air decreases because the warmer air is capable of holding more water.
Relative Humidity Is Based On Temperature
The relationship between temperature and humidity is often expressed by a percentage called relative humidity. Relative humidity is the ratio of water vapor present in air at a given temperature relative to the maximum amount of water vapor the air at that temperature could hold.
Practical Expressions Of Relative Humidity
Relative humidity at 100 percent denotes fog, rain, snow or other precipitation, where the air at that temperature can hold no more water vapor. Relative humidity at 6 percent denotes dry desert-like conditions where the air at that temperature contains only trace amounts of water vapor.