<P> Given that all the other factors influencing humidity remain constant, at ground level the relative humidity rises as the temperature falls . This is because less vapor is needed to saturate the air so, vapor condenses as the temperature falls . Dew point temperature is never greater than the air temperature because relative humidity cannot exceed 100% . </P> <P> In technical terms, the dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates . At temperatures below the dew point, the rate of condensation will be greater than that of evaporation, forming more liquid water . The condensed water is called dew when it forms on a solid surface, or frost if it freezes . The condensed water is called either fog or a cloud, depending on its altitude, when it forms in the air . </P> <P> A high relative humidity implies that the dew point is closer to the current air temperature . A relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water . When the moisture content remains constant and temperature increases, relative humidity decreases . </P> <P> General aviation pilots use dew point data to calculate the likelihood of carburetor icing and fog, and to estimate the height of a cumuliform cloud base . </P>

Relative humidity calculation from dew point and temperature