Fog

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface.

It forms precipitation in the form of rain and aerosols in the form of fog.

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface.

Examples of natural aerosols are fog, dust, forest exudates and geyser steam.

For aviation purposes in the UK, a visibility of less than 5 km but greater than 999 m is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported.

The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand, and snow.

Fog commonly produces precipitation in the form of drizzle or very light snow.

Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate.

Fog can be considered a type of low-lying cloud, usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions.

Conductive, radiational, and evaporative cooling require no lifting mechanism and can cause condensation at surface level resulting in the formation of fog.

Examples of this phenomenon include the Tule fog.

Tule fog is a thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of California's Central Valley.

Fog forms when the difference between air temperature and dew point is less than.

In the air, the condensed water is called either fog or a cloud, depending on its altitude when it forms.

By definition, fog reduces visibility to less than 1 km, whereas mist causes lesser impairment of visibility.

Fog and smoke can reduce visibility to near zero, making driving extremely dangerous.

Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass.

These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region.

It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast (see San Francisco fog).

The frequency of fog and low-lying stratus clouds is due to a combination of factors particular to the region that are especially prevalent in the summer.

It is common as a warm front passes over an area with significant snow-pack.

Fog can also occur preceding a warm frontal passage.

The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier.

Fog will form within a marine layer where the humidity is high enough and cooling sufficient to produce condensation.

For aviation purposes in the UK, a visibility of less than 5 km but greater than 999 m is considered to be mist if the relative humidity is 95% or greater; below 95%, haze is reported.

It may also correspond to the possibility of dew or fog forming, within a space that lacks temperature differences among its portions, for instance in response to decreasing temperature.

Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair.

Ice fog is a type of fog consisting of fine ice crystals suspended in the air.

It can be associated with the diamond dust form of precipitation, in which very small crystals of ice form and slowly fall.

Diamond dust is similar to fog in that it is a cloud based at the surface; however, it differs from fog in two main ways.

By definition, fog reduces visibility to less than 1 km, whereas mist causes lesser impairment of visibility.

One difference between mist and fog is visibility.

Fog begins to form when water vapor condenses into tiny liquid water droplets that are suspended in the air.

Fog and clouds form through condensation around cloud condensation nuclei.

Radiation fog is formed by the cooling of land after sunset by infrared thermal radiation in calm conditions with a clear sky.

One disadvantage of infrared imagery is that low cloud such as stratus or fog can be a similar temperature to the surrounding land or sea surface and does not show up.

Freezing fog, which deposits rime, is composed of droplets of supercooled water that freeze to surfaces on contact.

Hard rime is a white ice that forms when the water droplets in fog freeze to the outer surfaces of objects.

Sea smoke, also called steam fog or evaporation fog, is the most localized form and is created by cold air passing over warmer water or moist land.

Sea smoke, frost smoke, or steam fog, is fog which is formed when very cold air moves over warmer water.

Garúa fog near the coast of Chile and Peru, occurs when typical fog produced by the sea travels inland, but suddenly meets an area of hot air.

Although used in other contexts in the Spanish-speaking world, garúa most importantly refers to the moist cold fog that blankets the coasts of Peru and northern Chile, especially during the southern hemisphere winter.

Low-pitched notes are less affected by fog and travel further, which is why foghorns use a low-pitched tone.

A foghorn or fog signal is a device that uses sound to warn vehicles of navigational hazards like rocky coastlines, or boats of the presence of other vessels, in foggy conditions.

Temperature effect: A fog can be caused by a temperature inversion where cold air is pooled at the surface which helped to create the fog, while warmer air sits above it.

With sufficient humidity in the cooler layer, fog is typically present below the inversion cap.

Frozen fog (also known as ice fog) is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair.

This can be observed in foggy weather, when the temperature drops during the night.

Particularly foggy places include Hamilton, New Zealand and Grand Banks off the coast of Newfoundland (the meeting place of the cold Labrador Current from the north and the much warmer Gulf Stream from the south).

The cold Labrador Current mixes with the warm waters of the Gulf Stream here, often causing extreme foggy conditions.