Dew Point Temperature

The value highlighted in yellow located in the lower left corner (in the diagram above) is the dew point temperature in degrees Fahrenheit.  In this example, the reported dew point temperature is 56 degrees.

Dew Point Temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation.  Dew points provide insight into the amount moisture in the air.  The higher the dew point temperature, the higher the moisture content for air at a given temperature.

When the dew point temperature and air temperature are equal, the air is said to be saturated.  Dew point temperature is NEVER GREATER than the air temperature.  Therefore, if the air cools, moisture must be removed from the air and this is accomplished through condensation.  This process results in the formation of tiny water droplets that can lead to the development of fog, frost, clouds, or even precipitation.

What to Look For in Dew Point Observations:

• Relative Humidity can be inferred from dew point values.  When the air and dew point temperatures are very close, this indicates that the air has a high relative humidity.  The opposite is true when there is a large difference between air and dew point temperatures, which points to air with a low relaitve humidity.

• Look for locations with high relative humidities (or where the difference between air and dew point temperatures is small).  This indicates that the air is nearly saturated with moisture; clouds and precipitation are therefore quite possible.

• Look for locations with high dew point values (65 or greater).  Conditions at these locations are likely to be uncomfortably humid.