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Causes Of Low Visibility

Fog, Haze, Smoke, and Smog are four forms of ground based weather hazards that create low visibility.

Fog
Radiation Fog:	A very common form of fog also known as Ground Fog. It forms over fairly level land areas on clear, clam, humid nights. As the surface cools by radiation, the adjacent air is also cooled to its dewpoint. It usually occurs in stable air associated with a high pressure system.
Advection Fog:	When a low layer of warm, moist air moves over a cooler surface. Most common under cloudy skies along coastlines. Winds up to 15 knots will intensify the fog. Above 15 knots, turbulence creates a mixing of the air, and the fog usually lifts. It can form rapidly during day or night, and is most common in winter.
Upslope Fog:	It forms when moist, stable air is forced up a sloping land mass. Like advection fog, upslope fog can form in moderate to strong winds, and under cloudy skies.
Precipitation-induced Fog:	This may form when warm rain falls through a layer of cooler air near the surface. Evaporation from the falling precipitation saturates the cool air, causing fog to form.
Steam Fog:	Also known as Sea Smoke, occurs as cold, dry air moves over comparatively warmer water. It rises upward from the water's surface and resembles rising smoke. It is composed entirely of water droplets that often freeze quickly and fall back into the water as ice particles.

Haze:	Caused by a concentration of very fine salt or dust particles suspended in the air. It occurs in stable atmospheric conditions with relatively light winds.
Smoke:	Usually much more localized, it is generally found in industrial areas.
Smog:	A combination of Smoke and Fog, Blowing dust and blowing snow present similar problems. Smog occurs in moderate to high winds and can extend to an altitude of several thousand feet.