Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.įog commonly produces precipitation in the form of drizzle or very light snow. However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. This occurs from either added moisture in the air, or falling ambient air temperature. įog normally occurs at a relative humidity near 100%. 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. Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds. Some examples of ways that water vapor is condensed include wind convergence into areas of upward motion precipitation or virga falling from above daytime heating evaporating water from the surface of oceans, water bodies, or wet land transpiration from plants cool or dry air moving over warmer water and lifting air over mountains. įog begins to form when water vapor condenses into tiny water droplets that are suspended in the air. Those outside the camera lens's depth of field appear as orbs.įog forms when the difference between air temperature and dew point is less than 2.5 ☌ (4.5 ☏). A close-up view of water droplets forming fog. Their motion trails are captured as streaks.

See also: Cloud physics Minute droplets of water constitute this after-dark radiation fog, with an ambient temperature of −2 ☌ (28 ☏). įor aviation purposes in the United Kingdom, a visibility of less than 5 km (3.1 mi) but greater than 999 m (3,278 ft) is considered to be mist if the relative humidity is 95% or greater below 95%, haze is reported. īy definition, fog reduces visibility to less than 1 km (0.62 mi), whereas mist causes lesser impairment of visibility. The term fog is typically distinguished from the more generic term cloud in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes). Fog is similar to, but less transparent than, mist. Sea fog, which shows up near bodies of saline water, is formed as water vapor condenses on bits of salt. During condensation, molecules of water vapor combine to make tiny water droplets that hang in the air. In turn, fog affects many human activities, such as shipping, travel, and warfare.įog appears when water vapor (water in its gaseous form) condenses. 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. Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface.

Fog weather angwin