ELI5: Why does fog happen?

Imagine you're taking a warm bath. See all that steamy air above the water? That's water turning into a gas called water vapor.

Fog is kind of like that, but happening outside!

Here's the simple version:

1. Warm, moist air: Think of a warm, wet towel. It holds a lot of water. The air does the same thing.
2. Cooling down: Now, imagine you put that wet towel in a cold room. The air around it gets cooler. When warm, moist air cools down, it can't hold as much water vapor anymore.
3. Condensation: The extra water vapor turns back into tiny, tiny droplets of liquid water. It's like the steam from your bath turning into little water drops on the mirror.
4. Hanging in the air: These tiny water droplets are so light, they float in the air! We see them as a cloud near the ground – that's fog!

• The ground cools down overnight.
• This cools the air near the ground.
• If the air is moist, fog forms!