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Whiteout is a weather condition in which visibility and contrast are severely reduced by snow or sand. The horizon disappears completely and there are no reference points at all, leaving the individual with a distorted orientation. Whiteout has been defined as: "A condition of diffuse light when no shadows are cast, due to a continuous white cloud layer appearing to merge with the white snow surface. No surface irregularities of the snow are visible, but a dark object may be clearly seen. There is no visible horizon."〔''The Crossing of Antarctica'' by Sir Vivian Fuchs and Sir Edmund Hillary (Glossary, page 296) Cassell, London, 1958〕 A whiteout may be due simply to extremely heavy snowfall rates as seen in lake effect conditions, or to other factors such as diffuse lighting from overcast clouds, mist or fog, or a background of snow. People can be lost in their own front yards during a true whiteout, when the door is only away , and they would have to feel their way back. Motorists have to stop their cars where they are, as the road is impossible to see. Normal snowfalls and blizzards, where snow is falling at /h), or where the relief visibility is not clear yet having a clear field of view for over , are often incorrectly called whiteouts. ==Types== There are three different forms of a whiteout: # In blizzard conditions, snow already on the ground can become windblown, reducing visibility to near zero. # In snowfall conditions, the volume of snow falling may obscure objects reducing visibility to near zero. This only happens during lake-effect snow, or mountain-effect snow, where the volume of snow can be many times greater than normal snows or blizzards. # Where ground-level thick fog exists in a snow-covered environment, especially on open areas devoid of features. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Whiteout (weather)」の詳細全文を読む スポンサード リンク
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