Every time I read about it it trails into complex physics
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The dew point is when air gets cool enough outside to get the vapor water (humidity, clouds) to condense into liquid water. That liquid water forms on surfaces (usually plants you’ll see it most clearly) in little droplets we call “dew”
Air can hold a certain amount of water vapor in it. The amount it can hold depends on its temperature. Hot air can hold more water than cold air. If hot air is holding a certain amount of water vapor without an issue, but cools down, eventually it’ll reach a temperature it can no longer hold that amount of water vapor in it. That temperature is called the dew point.
The water no longer being held in the air means it collects on whatever surfaces it’s touching, creating dew, hence the name
Edit: typo
The dew point is the temperature of the air at which dew starts to appear. Dew is liquid water which condenses out of the water vapor contained in the air. You can often see dew in the early morning on blades of grass and other thin exposed objects. The dew point at any time depends on current atmospheric pressure and air humidity, which are the properties of the air.
It’s the temperature your glass of water needs to be for water to form on the outside of the glass.
As others noted, air can hold more or less water in it largely based on the temperature. So in a given place and time, there is a temperature where the water will come out of the air. You can see it on your glass of ice water amd on the grass or your car some mornings,.
On hot days, the dew point will impact how hot you feel (think heat index). The more humid it is, the higher the dew point, and generally the more uncomfortable you are in a given warm temperature.
Example:
Today it’s 64 F and humidity is 78%
Dew point is 45F (I completely made this number up for the example)
If you cool the air you have at this moment, down to 45F, you get fog/dew.
The reason is hot air can host more humidity than cold air. If the hair is full of water and it cools, the water will be expelled by the air. And you get wet even if it’s not raining. Dew point is a quick reference for the complex calculation. Someone does the math for you, and just tell you how far colder you need to get today before you get dew.
Most importantly, when you are below icing temperature, getting to dew point means you get sudden ice over things, as water is expended by air, below the freezing point. So ice is suddenly “coming out of the air”. For example, plane wings, wind turbines, power cables, even roads in a very windy day can get a dangerous ice layer quickly from passing the dew point. The more air movement there is (bind or vehicle movement) the quicker it builds up.
It’s a good reference to know how far, therefore how likely, you are gonna be affected by dew, fog, or icing.
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