Obscuration Types

An obscuration is any phenomena in the atmosphere, other than precipitation, that reduces the horizontal visibility. The most common obscuration "seen" is usually fog. Obscurations include...

Mist

Visible minute water particles suspended in the atmosphere that reduces visibility to less than 7 miles (11 km) but greater 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) which are based at the Earth's surface and reduces horizontal visibility to less than 5/8th mile (1 km) and, unlike drizzle, it does not fall to the ground.

Smoke

A suspension in the air of small particles 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 the larger particles have settled out and the remaining particles have 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 have occurred at or far away from the station which 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 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 dewpoint is greater than 3°F (1.7°C) then the obscuration is usually called 'haze'.

Next: Other Weather Phenomena