Fog is a cloud in contact with the ground.

Fog differs from other clouds only in that fog touches the surface of the Earth.

The same cloud that is not fog on lower ground may be fog where it contacts higher ground such as hilltops or mountain ridges. The foggiest place in the world is the Grand Banks off the island of Newfoundland, Canada.

Fog is frequent here as the Grand Banks is the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south.

The foggiest land areas in the world are Point Reyes, California and Argentia, Newfoundland, both with over 200 foggy days a year.

Most types of fog form when the relative humidity reaches 100% at ground-level.

Fog can form suddenly, and can dissipate just as rapidly, depending what side of the dewpoint the temperature is on..

For more information about the topic Fog, read the full article at Wikipedia.org, or see the following related articles:

Inversion (meteorology) — A temperature inversion is a meteorological phenomenon in which air temperature increases with height for some distance above the ground, as opposed ...  > read more

Cloud — A cloud is a visible mass of condensed droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary ...  > read more

Precipitation (meteorology) — In meteorology, precipitation is any form of water that falls from the sky as part of the weather to the ground. This includes snow, rain, sleet, ...  > read more

Humidity — Humidity is the concentration of water vapor in the air. The concentration can be expressed as absolute humidity, specific humidity, or relative ...  > read more

Related Stories

Fog Has Declined in Past Century Along California's Redwood Coast (February 16, 2010) — An analysis of newly available climate data shows that summer fog along the California coast has declined significantly in the past century, though it is unclear whether this is a natural variation ...  > read more

Team Describes Unique Desert Cloud Forest (September 18, 2006) — Trees that live in an odd desert forest in Oman have found an unusual way to water themselves by extracting moisture from low-lying clouds, MIT scientists report. In an area that is characterized ...  > read more

Eco-Friendly Self-Cleaning Material Tough On Stains, Light On Effort (August 25, 2009) — Scientists are reporting development of a new coating for glass, plastics and a range of other materials that would enable consumers to wipe away oils with plain water. They note that the material ...  > read more

Pentagonal Ice Discovered: Could Be Used To Modify Weather (April 7, 2009) — Scientists at the University of Liverpool have discovered a five-sided ice chain structure that could be used to modify future weather ...  > read more

Haze Dynasty: In China, Cloud-Free Days Do Not Mean Sunshine; Smog Is To Blame (January 18, 2006) — Despite decreasing cloudiness in China over the past half century, a new Pacific Northwest National Laboratory study in Geophysical Research Letters shows that less sunlight is reaching land. The ...  > read more

Search ScienceDaily

Fog Cleans Air Pollution