Why Does Fog Form?

It’s hard to tell smog from fog when one lives in a busy city. The best time for viewing for is before sun rise in the countryside. Fog is used in movies for different roles, they can create suspense or can lead to a flash back. Although it’s a fact that fog is real and they are made up of something.

Basically, fog comes from a cloud that has come near the surface of the earth and it is formed in the same way as a cloud.

fog Why Does Fog Form?

How fog is formed

Water is present on many bodies of water on the earth’s surface which evaporates. It can be evaporated from lakes, rivers and seas. Water evaporates in the form of water vapor, as it rises it turns into gas blending with dust and other little particles. It results in a water droplet. These droplets stick together and then fog is formed.

Sometimes, there is a mist which is thinner than fog. When water evaporates from the rivers, oceans and other sources of water, they give off water vapor which is a type of gas that bonds to dust particles as it rises up in the air. Water droplets are caused by this. When the water droplets group together, a cloud or some fog can be formed. Mist is also like fog but it is not as thick as fog.

Fog is formed when humidity rises to almost 100%. Besides that, the formation of fog requires that the difference between dew point and the air temperature should be 5 degrees F or slightly lower. Water droplets jell together in this condition becoming too heavy to rise any higher.

Types of fog

There are nearly twelve kinds of fogs. The most common are ground fog, radiation fog, steam fog, valley fog and evaporation fog.

When land cools off after sunset, radiation fog is formed. The sky’s thermal radiation causes this cooling effect. Ground fog is caused when the sky appears unclear and cloudy, it can hide about 60% of the sky. Steam and evaporation fog are almost the same. They are formed when cold air passes over a wet area of land and crosses over humid water.

The valley fog, as its name tells that it is formed over valleys and mountains at the start of winter. The temperature reverse causes this in which cold air descends on the valley while warm air rises up to the mountains.

It does not matter whether the terrain is jagged, flat or stiff, fog will form anyway. The topography of the place does not affect them. Sky, moisture and winds are the only conditions that lead to the formation of fog. Fog may not form in some in some cases when the terrain is flat or jagged with even the presence of light winds. Light winds hold back fog formation over a flat area but they can be formed over places that are far away from light winds.

City fog

City fog and smog fog should not be confused with each other. City fog is seen over cities like over the skies of Los Angeles and that is because LA has a number of upslope areas. Upslope fogs can be seen over Rockies. They need a warm surface below and brisk winds above.

There are strong winds on the western side of Los Angeles that meets up with the eastern winds coming from Denver. As the wind goes up the slopes of LA, it cools down beyond the dew point thus forming a fog. But when the wind goes out, the fog goes with it.

While it is nice to look at city fog, one should not breathe it in unless he is in a mood of getting sick.

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