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What is dew point?

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The dew point marks the temperature at which water vapor will turn into liquid water droplets. This process is called condensation. Condensation is what causes clouds to form, which can then lead to precipitation such as rain, snow, and hail. The dew point will always either be the same or lower than the actual outside temperature.

At the bottom of this illustration is a small translucent cube. Next to this cube are the words "Surface, Temperature, Dewpoint", showing that, at the surface of the Earth, the temperature is 87℉ and the dew point is 65℉. A yellow arrow pointing upwards points at a medium-sized translucent cube in the middle of the illustration, showing a growing rate of saturation in this block of air. This cube is labeled with the same words, describing that this block of air is at 2,000 feet with a temperature of 76℉ and a dew point of 65℉. A second yellow arrow points upward from the medium-sized cube toward a larger translucent cube with a white cloud inside of it. Next to this cube are the same words, describing that this cube is at 4,000 feet with a temperature of 65℉ and a dew point of 65℉. Again, this drawing shows how in an ideal atmosphere, the saturation level of a block of air containing water vapor with a surface temperature of 85℉ and a dew point of 65℉ will cool to the saturation point at about 4,000 feet in elevation. At this elevation, with the temperature and dew point being equal, a water vapor will condense and form a cloud.

This drawing shows how water vapor will condense and turn into a cloud when the dew point and temperature are equal. Image credit: NOAA/JPL

The higher the dew point rises, the greater the amount of moisture in the air. This affects how “comfortable” it will feel outside. So, just reading the relative humidity can be misleading.

Quiz time! Which combination do you think would feel more humid? A 30℉ day with a relative humidity of 100%? Or an 80℉ day with a relative humidity of 50%?

Ready to check your answer? It would feel much more humid on the 80℉ day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.

This digital graphic is labeled "Dew Point". On the left is a square outlined in red with small circles scattered across the square’s area. These circles represent molecules of water in warm air. On the right is a square outlined in dark blue, representing cool air. Inside this square are a few molecules of water with three big water droplets, representing molecules of water in cold air that condense into larger droplets.

Dew point marks the temperature at which water vapor will turn into liquid water droplets. As air cools, moisture condenses into droplets. Credit: NOAA/JPL

So, if you want to know just how “dry” or “humid” it will feel outside, look at the dew point instead of the relative humidity. The higher the dew point, the muggier it will feel.

Check out the chart below to see the general comfort levels using dew point that can be expected during the summer months!

Dew PointFeeling
Less than or equal to 55Dry and comfortable
Between 55 and 65Becoming “sticky” with muggy evenings
Greater than or equal to 65A lot of moisture in the air, very humid and uncomfortable
This digital graphic compares low dew point and high dew point. On the left is a drawing labeled "Low Dew Point". In this cartoon, a character is standing outside. Around the character are three water molecules. The cartoon says, "Sweat evaporates easily because there is room in the air for more water vapor molecules". On the right is a drawing labeled "High Dew Point". In this cartoon, the same character is sweating a lot and there are a lot of water molecules around them. The cartoon says, "Sweat builds up and won’t evaporate because the air is already full of water vapor molecules".

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