Obscuration Types
An obscuration is any phenomena in the atmosphere, other than precipitation, that reduces the horizontal visibility. The most common is fog. Obscurations include:
Mist
Visible minute water particles suspended in the atmosphere that reduce visibility to fewer than 7 miles (11 km) but more than or equal to 5/8thmile (1 km). There is often not much difference in the appearance of 'haze' and 'mist'. When the difference between the air temperature and dewpoint is 3°F (1.7°C) or less then the obscuration is usually called 'mist'.
Fog
Visible minute water particles (droplets) at the Earth's surface that reduce horizontal visibility to less than 5/8th mile (1 km). Unlike drizzle, fog does not fall to the ground but remains suspended.
Smoke
Small particles suspended in the air and produced by combustion. A transition to haze may occur when smoke particles have traveled great distances, 25 to 100 miles (40 to 160 km) or more. When larger particles settle out and the remaining particles become widely scattered through the atmosphere.
Volcanic Ash
Fine particles of rock powder that originate from a volcano and that may remain suspended in the atmosphere for long periods.
Dust
Fine particles of earth or other matter raised or suspended in the air by the wind, that may restrict horizontal visibility.
Sand
Sand particles raised by the wind to a height sufficient to reduce horizontal visibility.
Haze
A suspension in the air of extremely small, dry particles that are invisible to the naked eye and sufficiently numerous to give the air an opalescent appearance. That is the scientific way of saying haze is air pollution. There is often not much difference in the appearance of 'haze' and 'mist'. When the difference between the air temperature and dew point is greater than 3°F (1.7°C) the obscuration is usually called 'haze'.
Obscuration Types