Way less humid – analysis

If you were outside this weekend and today, you may have noticed how much nicer it feels outside today, due to the lower humidity (a cold front went by). This is a great chance to show why meteorologists like to use dew point and not relative humidity and how much one degree change in dew point means to the humidity.

This morning at 6 am, the relative humidity was 90%. Yesterday, it was 84%! However, today as the overall amount of moisture has not moved much, the relative humidity has dropped to 44%. Warm air can hold more moisture than cool air, so the relative humidity changes with the temperature and the absolute humidity.

What is also interesting is that the relationship between dew point and absolute humidity is not a straight line. Check out the chart below, of absolute humidity (vapor density of water) vs. dew point.

Now, take a look at the change in dew point and water vapor density at Clay, Alabama since 6 pm yesterday. In absolute terms, there is only a little more than half as much water vapor in the air as yesterday!

Category: Met 101/Weather History