More on Dew Point


As discussed in class previously, the dew point temperature is a rough measure of how much water vapor is in the air. It turns out that this also relates to the fact that meteorologists have noted that there is a general correspondence between areas of high dew point (and, thus, high water vapor content at the surface) and the tendency for thunderstorms to form.


The relationship between dew point temperature and water vapor can be established experimentally or computationally. The results are summarized in the table below, which shows the amount of water vapor held in a kilogram air parcel with various dew point temperatures. You don't have to know these amounts, but do need to consider the implications.


Air Parcel Dew Point Temperature (oC)

Amount of Water Vapor (g) in an Air Parcel



4 g


8 g


16 g


32 g


64 g

















Classroom Exercise:


Anchorage, Alaska has a temperature of 50F (10C) and a dew point of 50F (10C).  Fort Worth, Texas has a temperature of 86F (30C) and a dew point of 86F (30C).


What is the relative humidity at Anchorage? ____________

What is the relative humidity at Fort Worth? ____________

If the air at both places is forced to rise and cool so that all the water vapor condenses out, how much water vapor would change to liquid at Anchorage?  ________  at Fort Worth? __________


If you assume that all the water vapor that condenses at the two places falls as precipitation, how much more precipitation would occur at Fort Worth than at Anchorage?  __________________