Why so Dry?

Written by: Brian Neudorff

Are you going through several tubes of ChapStick or using moisturizer several times a day? Well you wouldn't be alone and it is very common this time of year. Cold air, like the arctic air masses we have been experiencing, contains very little moisture. When that some cold arctic air is brought into your home then warmed to room temperature the relative humidity could be as low as 10 to 20 percent.

This is a great example of how the relative humidity is a function of temperature and the amount of moisture in the air. I talked about this in a previous blog post titled, "Why Don't You Show the Relative Humidity?" We measure the amount of moisture in the air with the dew point temperature. The dew point temperature is the temperature at which the air can no longer hold all of its water vapor, and some of the water vapor must condense into liquid water. At 100% relative humidity, the dew point temperature and the air temperature are the same, and clouds or fog can begin to form. As the air temperature get farther away from the dew point temperature the relative humidity drops. So in the winter if you have a dew point of 20 degrees and warm that same air to 70 degrees the relative humidity will be around 15% if the amount of moisture in the air doesn't change.