Why does fog form

Fog is, in essence, a stratus cloud that has touched the earth. In this way fog forms much along the same processes of standard clouds, though due to the presence of lower pressure systems in an area (often in cooler months with colder weather playing a major role in the process) the stratus cloud is pushed to the earth’s surface and collects in a much more tangible way than normally seen higher up in the atmosphere.

Fog and clouds are generally formed anywhere where large amounts of water is regularly evaporated, with places such as oceans, rivers, lakes or any other water source providing a ready supply of water to evaporate. As evaporated water rises in gas form is bonds to other microscopic pollutants in the air (such as dusts, pollens or other debris), forming tiny water droplets. These droplets form together into larger bodies and generate the appearance of clouds if done in the upper atmosphere or fog if done lower. By this vary same process rain is formed if the water droplets gain enough size to allow them to condense from gas form and regain a liquid structure.

In order for fog to form rather than rise to cloud level a number of meteorological conditions must be met, the first of which is that the humidity level be close to (though not quite) 100 percent in an area. By reaching 100 percent humidity water will simply re-form into a liquid and thus prevent fog from occurring, though at too low of a level there will not be enough water vapor in the air to generate a basis for the fog to form off of.

Once this condition is met the air temperature must be within 5 degrees Fahrenheit of the dew point to allow for the air to be cool enough for the water droplets to remain close to the earth and form yet not cool enough to return them to condensation or dew. If both of these are occur and there is an ample body of water nearby as well fog will form and be present at ground level – often occurring at night and in mornings before strong sunlight raises the air temperature and allows the water vapors to rise back into the air as a cloud.