What is fog?

Have you ever woken up to a morning so misty you could not see the end of your street? Everything looks soft and grey, like the world is wrapped in a cosy blanket. That blanket is called fog — and it is really a cloud that came down to the ground!

A cloud at your feet

High in the sky, clouds are made of millions of tiny water droplets floating together. Fog is exactly the same, only it sits right down here with us instead of way up high. When you walk through fog, you are walking through a cloud. How amazing is that?

How does fog appear?

The air around us is full of water vapour — water that has turned into an invisible gas. Warm air can hold lots of this hidden water. But at night the ground gets cold, and it cools the air just above it.

Cool air cannot hold as much water vapour. So the vapour turns back into tiny droplets that float in the air. All those droplets together are the fog you see!

Where it likes to hide

Fog loves cool mornings, calm air, and places near rivers, lakes and the sea, where there is lots of water to share. When the sun comes up and warms the air again, the droplets turn back into invisible vapour, and the fog quietly disappears.

Wonder fact: Some thirsty animals and even special nets in dry deserts catch fog droplets to collect drinking water from the air!