Why does fog appear?

How fog forms

Fog appears when warm, moist air cools down near the ground. Air always contains water vapor, but warm air can hold more moisture than cold air.

When the air cools, it cannot hold all the water vapor anymore. The vapor condenses into tiny water droplets, which float in the air close to the ground.

These tiny droplets form fog.

Fog often appears in the morning or evening, when the temperature drops quickly. It can also form near lakes, rivers, or after rain, when the air is very moist.

Fog is basically a cloud that forms at ground level.