The Current Dewpoint image shows the dewpoint
, contoured every 10 degree F, for the most recent hour. The dewpoint
(or dewpoint) is the temperature
to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor
to condense into water. The condensed water is called dew. The dewpoint
is a saturation point.
When the dew point temperature
falls below freezing
it is called the frost
point, as the water vapor
no longer creates dew but instead creates frost
or hoarfrost by deposition.
The dew point is associated with relative humidity
. A high relative humidity
indicates that the dew point is closer to the current air temperature
. If the relative humidity
is 100%, the dew point is equal to the current temperature
. Given a constant dewpoint
, an increase in temperature
will lead to a decrease in relative humidity
At a given barometric pressure, independent of temperature, the dewpoint
indicates the mole fraction of water vapor
in the air, and therefore determines the specific humidity
of the air.
The dew point is an important statistic for general aviation pilots, as it is used to calculate the likelihood of carburetor icing
, and estimate the height of the cloud base.