Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Temperature Effecting Dew Point
Name: Danielle
Status: student
Age:  14
Location: N/A
Country: N/A
Date: Friday, November 01, 2002


Question:
How does temperature effect the dew point?


Replies:
Danielle -

Temperature does not affect dew point. Dew Point is the temperature to which the air must be cooled before it becomes saturated. When it is saturated it is holding all the water vapor it is able to hold.

As you may know, warm air can hold more water than cold air. Or said another way, as air cools, it loses its ability to hold water. To what temperature would we have to cool the air in your back yard to have it holding all the water it can hold? That's the dew point.

If air continues to cool, the water vapor in the air has to condense (change into a liquid) or sublime (change into a solid). When it condenses it may form dew, clouds, fog, rain... when it sublimes it forms frost, snow...

Even though we use the same degrees to describe temperature and dew point, they are really different variables used to describe the atmosphere.

Larry Krengel


The dew point (the temperature at which moisture will condense out of the air) correlates with absolute humidity, and is not directly related to temperature. The only real impact temperature can have on the dew point is that the dew point cannot really be above the air temperature.

Richard E. Barrans Jr., Ph.D.
Director of Academic Programs
PG Research Foundation, Darien, Illinois


Danielle,

The temperature does not affect the dew point. The dew point temperature reflects the absolute amount of water vapor in the air. It is the temperature to which you must cool the air at constant pressure and constant water vapor content for saturation (relative humidity = 100%) to occur.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


Hi Danielle-

The dew point and temperature are pretty much independent of each other, except for this restriction...the dew point cannot be higher than the temperature. It can be the same, but not higher. The dew point is the temperature to which the air must be COOLED, in order to become saturated, or, 100 percent relative humidity.

The dew point is an indication of how much water vapor is in the air. The more water vapor, the closer the dew point is to the temperature. When the air becomes saturated, the dew point and the temperature are the same.

So it is really the HUMIDITY that affects the dew point, rather than the temperature.

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO


The dew point is a way of describing how much water vapor is present in air at a given temperature, so it is not so much that temperature affects the dew point, but the amount of water vapor in the air determines the dew point. The dew point is defined as the temperature where the amount of water vapor present in the air, expressed as a partial pressure is equal to the vapor pressure of water at that temperature. It can be related directly to the relative humidity, which measures the same thing but is expressed as the percentage of water vapor present in the air at the given temperature compared to the vapor pressure of water at that temperature. For example, if today we read that the dew point of the air is 44 degrees F. and the present temperature is say, 75 degrees F. It means that if the temperature were to fall to 44 degrees F. tonight then water would condense (forming dew). If the temperature were to only fall to say 50 degrees F. no dew would form.

Vince Calder


Click here to return to the Weather Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory