ELI5: Why does fog form more in the morning?

Imagine your bedroom window.

During the day, the sun warms up everything outside, like the ground, plants, and even the air. Think of it like baking a cake - the sun is the oven! The air becomes warmer, and warm air can hold more water vapor, like a sponge can hold more water.

But, when night comes, the "oven" turns off. The ground starts to cool down because it's not getting any more heat from the sun. This cooling also makes the air near the ground cooler.

Here's where the fog comes in:

• Cool air can't hold as much water vapor as warm air.
• So, as the air cools during the night, the water vapor starts to turn back into tiny water droplets. This is called condensation.
• These tiny water droplets float in the air, and when there are a lot of them, we see them as fog.

The ground is usually coldest just before sunrise because it's been cooling all night. This means the air near the ground is also at its coldest, and the most water vapor has condensed into fog.

As the sun rises, it starts to warm things up again. The air warms, it can hold more water vapor, and the fog slowly evaporates, turning back into invisible water vapor. That's why the fog usually disappears as the day gets warmer!