Relative Humidity is the measure of how much moisture is contained in the air. However, because this can change by temperature as well as the volume, it needs to be expressed as a ratio between the two. This ratio being; the actual amount of moisture in the air at a given time and the maximum amount that it could contain at that same temperature.
When air contains the maximum amount of moisture that it can hold, the relative humidity would be 100 percent. An increase in temperature would change the situation to where the relative humidity would decrease (to 70 percent for example). This change would allow more moisture to be added, which could take the level up to the 100 percent again. If this situation was to occur and moisture was added (up to its maximum) and the situation reversed, that is, the temperature was to drop, the moisture added would then be in excess of the 100 percent and would need to be shed as condensation and the amount shed would be relative to the temerature drop.
