31.   Powdery snow on the ground will be whipped into the air, reducing visibility to one-quarter of a mile or less for several hours.

32.   Ridge-top fog will reduce visibility below one-eighth of a mile on some mountains.

33.   Since then, federal and state regulators have clamped down on various air pollutants, including some chemicals that reduce visibility in national parks.

34.   Smoke reduces visibility, increases the amount of sunlight that is reflected to space, and encourages the formation of haze, as water vapor condenses onto smoke particles.

35.   The heavy rain, which had turned the dirt roads to mud, reduced visibility to a few feet.

36.   The move to cut back on British troops follows a series of other measures intended to reduce the visibility of British forces in Northern Ireland.

37.   The practice allows federal officials to reduce the visibility of sensitive operations by substituting paid civilians for American troops or career intelligence officers.

38.   The strong winds will cause blowing and drifting of the snow, reducing visibility to near zero at times.

39.   The territorial change of hands has also reduced the visibility of Palestinian women.

40.   The time of greatest risk is night, when visibility is reduced and judgment may be impaired by fatigue and possibly alcohol.