What is Dew Point?

Meteorologists often talk about it.  Have you ever wondered why it’s so important?  What is dew point anyway?  How does it affect us?  Well, it is a complex calculation that tells us quite a bit about the weather.  The following blog will provide a simple definition, a practical example, and some of the things that dew point can tell us.

Dew on a blade of grass in North Sarasota, FL.

Defined

Essentially, dew point is defined as the temperature that, under the right conditions, will produce condensation.  NOAA’s National Weather Service, defines it as the “temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form.”  If a surface is at the dew point and the air is close enough, moisture will form.  When the air cools beyond this point, precipitation forms.

A Practical Example

The Weather Dudes provide a great example.  Almost everyone has seen their breath on a cold, damp day.  This is literally dew point in action. When you breathe, the air coming out of your lungs is warmer than the air outside of your body.  Warmer air can hold more moisture than colder air. As your breath collides with the cooler air, the invisible water droplets immediately condense and form a cloud.  The reason is because the colder air cannot hold the water vapor at this cooler temperature.  It releases the vapor as tiny drops of moisture that stay suspended in the air.

Why Does Dew Point Matter?

There are several things that it tells us.

1. The saturation of the air (a great indicator of actual humidity)
2. How uncomfortable we might feel on a warm day
3. If we have to worry about frost
4. When to water our plants

Most people disregard dew point in the weather report, but this is because they don’t realize what it actually is.  With a better understanding, you will see that is something worth noticing.  Not only will your level of comfort be affected by this temperature, but your plants can be affected by it too.  So, it is more than just a random number to disregard.