Humidity Maps
National Dew Point
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Learn about Dew Point
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 fog, and estimate the height of the cloud base.
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