Everyday skies · surface phenomenon

Fog

A cloud you can walk into

Vallee-brouillard.jpg · Thomas Bresson · Original & credit · CC BY 3.0
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Trees in fog on the northern side of Loch Tay, Scottish Highlands, Scotland.jpg · Michal Klajban · Original & credit · CC BY-SA 4.0
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Fog around Lake Heron, Taylor Range, Canterbury, New Zealand.jpg · Michal Klajban · Original & credit · CC BY-SA 4.0
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Fog rolling over Arched Rock.jpg · Frank Schulenburg · Original & credit · CC BY-SA 3.0
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Spot it

Tiny suspended droplets reduce visibility near the ground.

How it forms

Air near the surface becomes saturated through cooling or added moisture.

Read the sky

Fog can strongly reduce visibility even without rain.

Where to look

Look in moist valleys, over cool water or where humid air meets a colder surface.

Little sky facts

Reveal fact 1
Fog forms at the surface.
Reveal fact 2
It obscures distant objects more than nearby ones.
Reveal fact 3
Cooling can bring air to saturation.
Reveal fact 4
Fog is an observing condition, not one of the ten cloud genera.

Try this

Compare near and distant silhouettes from a safe place.

Draw your own cloud ↗

Read a little deeper

WMO International Cloud Atlas

Conditions described here are places to look, not a global frequency ranking. Use local weather forecasts and warnings for decisions. Never look directly at the Sun.

Next sky story: Cumulus humilis →