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What Does Dew Point Mean?

  • Air Quality Facts
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You've heard the words dew point time and again, in forecasts and on weather sites - but may have never fully grasped the meaning of it. And considering the fact that you take careful measures to control the conditions inside your home, it's important to understand the role that outside dew point plays in your daily life.

If you've ever scratched your head over the term, here's a simple explanation of dew point and its significance.

What is Dew Point?
The first thing to know is that the warmer air becomes, the more water vapor it can contain. Sometimes the air is filled with so much of this invisible gas that it cannot hold it and the vapor condenses into liquid water. Air that's just above the ground, though, condenses into a fog. When air that's dense with water vapor hits physical objects, such as your car or blades of grass, it forms dew drops. The temperature - according to current humidity and pressure - below which those water droplets condense is the dew point. In other words, when relative humidity hits 100 percent, that's the dew point. 

Can it Change Over the Course of a Day?
What's so remarkable about dew point is that it can vary over just a few hours. According to USA Today, a significant change is especially likely if a front moves through, whether cold, warm or stationary. A front is the boundary between two air masses that vary vastly, typically by temperature.

How Can it be Measured?
The National Weather Service reported that you can measure dew point yourself with a thin metal or plastic cup, a thermometer, ice water and a large dropper. Simply head outside on a sprint or summer day, place a couple inches of warm water in a cup and measure the temperature to make sure it's around 80 degrees. Keep adding drops of ice water and stir while eyeing the temperature. When a thin film of water vapor forms on the outside of the cup, note the temperature - that's the dew point!

What Can Dew Point Indicate About Comfort Levels? 
Generally a dew point of 60 says that it's pretty humid outside, and at 70 things get uncomfortable, as the high concentration of vapor in the air makes it difficult for sweat to evaporate. Air conditioning, fans, staying out of the sun and wearing light, breathable clothing can help keep you cool. Additionally, it's a good idea to use an air purifier in your home if you live in a high-humidity region, as these conditions typically encourage growth of mold and bacteria, which can become airborne.