Weather Lab: What is dew point?

Posted on Oct-03-2016 at 00:00:00

It’s a dry heat!

If you have lived in Arizona for any time period, you have likely heard that saying. So how can you tell it’s really a dry heat? Easy, take a look at the dew point

Dew point is simply the temperature at which condensation will form. The higher the dew point, the more moisture present in the atmosphere.

For example: if the dew point is 55 degrees, the air temperature would need to fall to 55 degrees for condensation to form. 

Ever notice water form on the outside of your drink cup? That occurs as the cold contents inside your cup cools the container to the dew point, creating condensation. 

The same is true with dew and frost. Dew forms outside on your car, patio furniture, etc. because those objects cool to the dew point forming condensation. Frost forms the same way but freezes when the temperature falls below freezing.

The best part about dew point is that it is NOT dependent on the temperature. As a result, you can easily compare locations dew point. The one with the higher dew point has more moisture. The same is NOT true when talking about relative humidity as it is dependent on the temperature.  

Here in Phoenix, the dew point is normally very low. On the flip side, locations across the eastern United States often see dew points in the 60s and 70s.

So besides during monsoon, when the dew point is typically 55 degrees or higher, Arizona typically is a “dry heat."