I just don’t really get them is all
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Air has the ability to hold moisture.
Depending on the temperature, a given volume of air has a max limit on how much moisture it can hold. Lower temperature air has a lower limit, and higher temperature air has a higher limit.
You can measure air’s moisture content as some fraction of its max capacity. On a weather report, this would be called humidity.
A comprehensive weather report may also have something on there called “dew point”, expressed as a temperature in degrees. The dew point is the temperature where, if you chilled the outside air to that temperature, its max moisture-holding capacity will drop to match how much moisture is in the air right now. Drop the temperature of air *below* the dew point, and suddenly we have a problem. The max capacity of the air is lower than how much moisture is in the air.
The dew point gets its name from dew. The drips of water you’ll find on blades of grass early on a cool summer morning. At night, everything cools down, including the grass. In the morning, when the sun starts to come up, the air begins to warm up, allowing it to hold more moisture. But the grass is still cool. All the air very close to the grass cools down, below its dew point. The excess moisture in the air gets forced out, like wringing a wet sponge, depositing liquid water on the cool grass, AKA dew.
A very chilled drinking glass will “sweat” on the outside for the same exact reason–you could technically say your glass is covered with dew!
So, if you have a very cold object, it will chill the air around it below the air’s dew point, and form dew. What if we just cool down the air directly, without an object? This is where things get interesting. Water wants to be forced out of the air, but it has no object to deposit onto. Or does it? Air is filled with countless microscopic motes of dust. Moisture in the air will happily start to condense onto those if it has to. This creates a sea of countless tiny liquid water droplets, so small that they can remain suspended in the air. This phenomenon is what we know as fog!
Okay, last pieces of the puzzle: Warm air rises. As you rise in the atmosphere, the air pressure drops. And when gas pressure drops, its temperature decreases. So if you have a warm bubble of air near the ground that’s full of moisture, it’s gonna start rising. As it rises, it cools down. Eventually, there’s going to be some altitude where the air’s temperature hits its dew point. Above this invisible cutoff line, the rising air becomes a floating patch of fog. And that, my friend, is a cloud!
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