What is the “Dewpoint” and why is it important?
Dewpoint (or Dew Point Temperature) is a measure of atmospheric moisture. A higher dew point indicates more water vapour moisture present in the air. It is the temperature to which the air must be cooled in order to reach saturation (assuming air pressure and moisture content are constant), that is, when no more moisture can be absorbed and excess water vapour must be released as, for just one example, fog. In the UK a higher dewpoint relative to air temperature usually indicates an air mass of warm maritime / tropical origin and usually the temperature does not fall very much overnight. In hot summer weather a high water vapour content gives the uncomfortable “sticky” or “oppressive” feeling. A low dewpoint relative to air temperature suggests air imported from a cooler or cold, dry Polar / Continental source which feels “fresh” and can allow a deep fall of overnight temperature in calm conditions. Dewpoint is a more helpful measurement of air moisture than Relative Humidity % in many
