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Fog

✨ The Cloud that Touches Ground

Fog is a cloud that forms directly at ground level. It appears when tiny droplets of liquid water, or sometimes small ice crystals in very cold conditions, remain suspended in the air. This usually happens when humid air cools to its dew point, the temperature at which water vapor condenses into droplets.

Cooling can occur overnight as the ground loses heat, when warm moist air moves over a colder surface, or when water evaporates into cool air. Fog often develops in valleys, near lakes, rivers and coastlines, where moisture is abundant and the air is more likely to cool.

Meteorologists define fog as reducing horizontal visibility to less than one kilometer; when visibility is greater, the phenomenon is generally called mist. Different types of fog form under different weather conditions, including radiation fog, advection fog, upslope fog and evaporation fog.

Some fog disappears quickly after sunrise as the air warms, while other banks can persist throughout the day if cool, humid conditions remain. Dense fog can disrupt road, air and sea transport because it makes it difficult to see obstacles, vehicles and navigation markers. Although it may seem unpleasant, fog plays a role in the water cycle by returning moisture to the ground. In some dry coastal regions, it even provides an important source of water for plants, animals and entire ecosystems.

💡 Did you know?

Did you know that fog can be a very useful source of water? In some very dry deserts of South America, residents set up huge nets called 'fog catchers.' Tiny droplets crash into the net, gather, and flow through pipes to become drinking water. It's a real technological magic to help those who have no rain!

There's a very special fog called 'freezing fog.' It forms when it's very cold, but the water remains liquid. As soon as these droplets touch a tree, a bench, or a sign, they freeze instantly! Within minutes, the entire landscape is covered in a thin layer of white, sparkling ice. It looks like the Snow Queen has passed through!

San Francisco, in the USA, is famous for its thick fog that rolls in from the ocean. Residents love it so much they've given it a name: 'Karl'! He even has his own social media account. You can often see the red towers of the Golden Gate Bridge emerging from the white fog carpet, as if floating above an ocean of cotton.