Expert: Dave Dombek - 9/17/2008

Question
Hey Dave...I am working on my Masters thesis oh humid acclimation and I saw a
question answered about what defines high humidity vs low humidity.  I need to
find out at what point does it become "high" and when does that change from
being considered "low".  Thanks so much for helping me with this!

Answer
Jayme,

Humidity is a term that is really not well understood. The relative humidity depends on the difference, if any, between the temperature and the dew point. On most days, the relative humidity is actually highest in the morning when the temperature and the dew point (saturation temperature of the air) are very close or the same. That is why some days often start off with dew or even fog. However, as the air heats up during the day, the spread between the temperature and dew point widens and the relative humidity drops. That is what makes this term very confusing because at the time when it feels the most uncomfortable outside on a hot, summer day, e.g. at 3 p.m., the relative humidity is actually at a minimum then. A much better indicator of how much humidity or moisture there is in an air mass is dew point. The dew point is the temperature to which the air has to be cooled in order to get condensation. The higher the dew point, the more moisture there is in the air. Here is a good guide for dew points in the warmer seasons here in the U.S. , especially targeting the northern portions of the country.
Dew points in the 50s or lower: comfortable
Dew points between 60 and 65: moderately humid
Dew points between 65 and 70: humid
Dew points between 70 and 75: very humid, muggy, sticky, oppressive, etc.
Dew points over 75: tropical rain forest!

I hope this helped

Sincerely,

Dave