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The temperature to which air must be cooled at constant pressure to reach saturation is called dew-point temperature or simply dew point, Td. Further cooling will result in condensation of the excess moisture. Thus, dew point is a direct measure of the water vapor pressure. The difference between temperature and the dew point is a measure of the degree of saturation of air. The general application of dew point is made for estimation of precipitable water, height of cloud base, and forecasting of dew, fog, and frost. Following Linsley et al. (1989), the dew-point temperature can be estimated within 0.3C in the temperature range 40 to 50C as

 T - Td  = (14.55 + 0.114T)(1 - RH) + [(2.5 + 0.007T)(1 - RH)]3 + (15.9 + 0.117T)(1 - RH)14                 

 where T is in C, and RH is the relative humidity expressed as a decimal fraction.

The maximum persisting 24-hour dew point temperature (C) in India