National Weather Service United States Department of Commerce

Learning Lesson: Drawing Conclusions - Dew Point Temperature Map

Dew point temperature map.

This map shows the dew point temperature for various locations over the conterminous U.S. The values are in °F. Recall, dew point is the temperature to which, if the air cooled to this value, then the air would be completely saturated.


Using a green colored pencil, lightly draw lines connecting equal values of dew point temperatures, every 10°F. Remember, like isobars, these lines (called isodrosotherms) are smooth and do not cross each other.


You will draw lines connecting the dew point temperatures, much like you did with the air temperature map. However, you will also need to interpolate between values. Interpolation involves estimating values between stations which will enable you to properly analyze a map. Label the values. Your map should look like this.


Isodrosotherms are used to identify surface moisture. The closer the temperature and dew point are together, the greater the moisture in the atmosphere. As the moisture increases so does the chance of rain. Also, since moist air is lighter than dry air, the greater the moisture, the easier for the moist air to lift into the atmosphere resulting in a better chance for thunderstorms. Typically, dew point 70°F or greater have the potential energy needed to produce severe weather.