Skip to main content
Cloudy icon
66º

Dew point explained: Here’s why your windows often fog up in the summer

What is the dew point and how does it impact you?

Dew point. (WDIV)

ORLANDO, Fla. – Oftentimes in Florida, on a very humid morning, you may wake up with dew all over your car or house windows.

The answer as to why that is lies with the dew point or the temperature the air needs to be cooled to reach saturation, or a relative humidity of 100%.

A lot of times relative humidity is confused with dew point.

You may hear someone say on a very hot and humid afternoon, “It’s 95 degrees with 100% percent humidity.”

That’s not entirely accurate. More often than not, the relative humidity is in the 50-60% range in the afternoon. The relative humidity becomes lower the further the temperatures gets from the dew point.

[EXCLUSIVE: Become a News 6 Insider (it’s FREE) | PINIT! Share your photos]

What that person actually means is that it’s 95 degrees with high humidity. The dew point temperature in that scenario is likely in the upper 60s or 70s.

The higher the dew point in the afternoon, the more uncomfortable you feel. Typically during the heart of summer in Florida, the dew point temperature is in the mid- to upper 70s.

Dew point

Dew point is also critical for storms. When there is a higher dew point, there is more moisture in the atmosphere to fuel daily thunderstorms.

So what about the windows in the morning?

Condensation typically forms on the outside of your windows when it is hot and humid outside. The cooler air from inside the house or car cools the windows to lower than the dew point temperature.

When the water vapor in the outside air comes in contact with a surface temperature, in this case windows, that is lower than the dew point, saturation takes place. Dew then forms on the outside of your windows, making it difficult to see out of them.

This is similar to your cold beverage sweating in summer.

The colder you keep your house, the more often you will see condensation on the outside of your windows during the summer. The chances of this also rise when the dew point is extremely high on a very humid morning.