HOW IS DEWPOINT CALCULATED?
 
METEOROLOGIST JEFF HABY
Dewpoint is the temperature air will reach saturation when air cools and maintains a constant pressure
and constant moisture content.
To find dewpoint, the temperature and
wet bulb temperature need to be known. The temperature is read straight
from a thermometer. The wet bulb temperature is the temperature air will cool to when complete evaporative
cooling occurs. Getting the wet bulb temperature requires the use of a psychrometer or hygrometer. Once you have the
temperature and wet bulb temperatures use one of the methods below to determine the dewpoint:
1. Find a chart that will give you dewpoint when temperature and wetbulb are known. Some charts will require
the wetbulb depression. The wetbulb depression is the temperature minus the wetbulb temperature.
2. On the SkewT LogP, plot the temperature and wetbulb temperature at the pressure level it is being measured.
Draw a line parallel to the dry adiabates through the temperature and draw a line parallel to the moist adiabates
through the wet bulb. These two lines will intersect. At the intersection, drop a line down parallel to the mixing
ratio back down to the original pressure level. This value is the dew point.


