What is Dew Point?

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Water vapor is added to the atmosphere through evaporation and transpiration.  At some point, however the air becomes SATURATED or full of water.  

At this point, the relative humidity is 100%, the wet bulb and dry bulb are the same, evaporation stops, and water vapor must come out of the air.

Under these conditions CONDENSATION occurs.

DEW POINT

DEW POINT IS THE TEMPERATURE AT WHICH CONDENSATION BEGINS.

As soon as the air temperature reaches the dew point water vapor will begin to condense.  We measure the dew point temperature with a psychrometer in the exact same way as we measure relative humidity.  The only difference is we use a different chart.

What is the Relationship between Dew Point and Relative Humidity?

Both dew point and relative humidity are important weather data to track because they help us make predictions about the probability of precipitation.

WHEN THE AIR TEMP AND DEW POINT ARE CLOSE TOGETHER THAT MEANS:

  • Relative Humidity is High
  • Condensation is occurring
  • It is likely to rain

WHEN THE AIR TEMP AND DEW POINT ARE FAR APART THAT MEANS:

  • Relative Humidity is Low
  • Evaporation is occurring
  • It is likely clear and sunny