What is dew point? Dew point definition

The dew point temperature is the temperature at which the liquefaction process of the gas or the selected component of the gas mixture can start at a given pressure, and in the case of a gas mixture, also at a given composition. The gas component under consideration (eg steam) has a partial pressure at a given temperature equal to the pressure of the saturated vapor of this component at the dew point temperature.

In the case of water vapor in the air, it is the temperature at which the water vapor contained in the air reaches the saturated state due to cooling (with the existing composition and air pressure), and below this temperature it becomes oversaturated and condenses or resublizes. When the saturation level is reached, mists, clouds, precipitation and latent rainfall arise.


How to calculate dew point

The approximate formula used to determine the dew point temperature:

td – dew point temperature [° C]

t – temperature [° C]

H – relative humidity in%


How is dew point measured

The dew point temperature determines how much you need to cool the surface located in a specific center with the air, so that water begins to condense on it.


It depends mainly on:

relative humidity (RH)

and its temperature (T).


This phenomenon is easier when the relative humidity of the air is higher.

This means that for high relative humidity, the dew point temperature is high (not much different from the actual temperature of the medium).

It is worth noting that the dew point temperature depends on the pressure prevailing in the medium (the higher the pressure, the lower the dew point), but in most practical situations it is sufficient to take into account temperature and relative humidity, which in themselves take into account the dependence on pressure.


Dew point in weather forcasting

The dew point temperature is of great importance in meteorology, and in particular in aviation meteorology, as it is directly related to the altitude where the cloud base is located in given meteorological conditions. The height of the cloud base is, however, crucial in thermal flights (gliding, hang gliding, paragliding) because it is, under normal conditions, the upper limit for an aircraft rising in the thermal chimney.