What is humidity?
Another word for humidity, is the moisture that present in the air.
The higher the outside air temperature (OAT) the more humidity (moisture) it can hold and vice versa.
If you look at a weather clock, most of them tell you the moisture level currently present within the air
surrounding you. For example, if it says 70%, that means that 70% of a given amount of air are moist,
or close to being water. 30% are still dry of that given amount. You can feel that heavy moist air, especially
when you are located at areas close to the equator.
That’s also the part where Dewpoint comes into play. The closer a temperature cools down to its dewpoint,
the more moist it will become. If air cools down to about 2-3 degrees above it’s dewpoint, it’s very close to being
saturated. What does that mean? Saturated means, the air will now show up as tiny water drops, because a given amount of air now holds ~ 100% of it’s possible moisture. In other words, the relative humidity is now 100%.
The best example for this is clouds. Air leaving or radiating from the ground will cool down until it has reached
it’s Dewpoint. This is usually observable as the cloud base.