WHAT IS RELATIVE HUMIDITY? HOW DO YOU MEASURE RH?
That miserable, oppressive feeling you experience while outdoors on muggy summer days is not necessarily caused by heat. Most likely, that energy-sapping sensation can be blamed on humidity.
Since the human body cools when perspiration evaporates, the higher the humidity is, the less likely sweat will evaporate. That’s why people are so sensitive to the effects of humidity and why humidity is frequently mentioned in weather reports.
Meteorologists usually refer to the atmosphere’s relative humidity (RH). In order to understand RH, it is essential to first grasp the concept of absolute humidity (AH).
Absolute humidity is defined by Merriam-Webster as “the amount of water vapor present in a unit volume of air.” The warmer the air, the more moisture it can contain.
Relative humidity is “the ratio of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature.”
RH is expressed as a percentage.
A reading of 100 percent RH means the air is completely saturated with water vapor. When rain occurs, the RH is 100 percent at the altitude where clouds form but the humidity near the ground level may be much lower.
The comfort level differs among people, but most individuals feel most comfortable in an environment with an RH between 40-60 percent.