Dew Point or Relative Humidity Determines Discomfort?

Chief Meteorologist Grant Gilmore explains how Dew Point helps better determine comfort than Relative Humidity

GREENSBORO, N.C. -- During the summer months you often have to consider three things before stepping outside. The first thing is whether or not it is going to storm. And the second and third things are how hot and humid is it going to be. Humidity, or at least what we typically think of with humidity, ultimately is a factor of how comfortable we feel while outside.

Unfortunately, the measurement of humidity (Relative Humidity) is not the best way to gauge how moist or dry the air will feel. In fact, Dew Point is a better indicator of how comfortable it is going to feel outside.

Relative Humidity is defined as; The amount of moisture present in the atmosphere RELATIVE to the amount of moisture needed for the air to become saturated. This relative relationship in moisture present and moisture needed to saturate the atmopshere is primarily dependent on temperature. Simply put, cooler air does not 'hold' as much moisture as warmer air. For example, it doesn't take as much moisture to create 100% Relative Humidity when the temperature is 40°F as it does when the temperature is 80°F.

The better indicator of comfort and moisture in the atmosphere is the Dew Point. The Dew Point is the ABSOLUTE measure of atmospheric moisture at a given time. The Dew Point is also the temperature at which the air must be cooled in order for the water vapor in the air to condense and form into dew.

Simply put, a higher Dew Point indicates more moisture in the atmosphere. As a result, the more moisture that is in the air the less water (sweat) is able to evaporate (cool your body) into the atmosphere. This ends up being the determining factor in how 'humid' or comfortable you feel.

When Dew Point temperatures are in the 50's the air typically feels fairly pleasant. As Dew Point temperatures climb into the 60s we typically begin to feel a little 'humid'. It's when Dew Point temperatures climb above 65°F that it will feel sticky outside. And finally, when Dew Point temperatures surpass 70°F the atmosphere truly feels tropical and oppressive.

So, in the future when you are trying to figure out how 'humid' it is outside, reference the Dew Point instead of the Relative Humidity.

If you have a weather question that you would like answered in the 2 Wants To Know Newscast send it to Chief Meteorologist Grant Gilmore on twitter, facebook or email.


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