DEW-POINT TEMPERATURE
A temperature less frequently reported on radio or TV is the dew-point
temperature. This is the temperature that a sample of air would have
if it was cooled until dew (or frost) began to form on a surface
immediately adjacent. As you can see, this "temperature" is really a
round-about way of saying something about the amount of moisture or
humidity in the air. If the dew-point temperature (sometimes we just
call it the "dew point", for short) is close to the air temperature,
the relative humidity is high, and if the dew point is well below the
air temperature, the relative humidity is low. If moisture condenses
on a cold bottle of pop taken out of the refrigerator, the dew-point
temperature of the air in the room is above the temperature of the pop
bottle. This happens much more frequently in summer than winter, when
there is generally more moisture in the air.
Incidently, one of the clues a meteorologist uses for forecasting
tonight's low temperature is to look at today's dew point: if no fronts
are expected to come through, tonight's low temperature will not get
much below today's dew point. (Unfortunately, not all forecasting is
that simple.) The dew-point temperature is measured in the same
enclosure as the air temperature.