The original definition of whiteout in the American Heritage® Dictionary was based on the term’s use by polar explorers. In this sense, the word refers to a weather condition caused by a heavy cloud cover over snow, in which the light coming from above is approximately equal to the light reflected from below, and in which the evenness of the lighting results in the disappearance of visual cues such as shadows or a visible horizon. But when laypeople and TV meteorologists use the term whiteout, they typically mean a very different weather condition, in which heavy windblown or falling snow reduces visibility almost to zero.
Both conditions result in a visual field which is mostly or entirely white, but there are several important differences between them. In the first kind of whiteout, there needn’t be any snow in the air; the effect is solely a result of the way the snow cover on the ground is illuminated evenly by light filtering through the clouds overhead. Nonwhite objects in one’s field of view are visible even at a great distance, but it may be hard to identify them at first because the lack of visual cues makes it hard to tell how far away they are or whether they’re above or below the horizon. The second type of whiteout, the type laypeople are more likely to be familiar with, occurs only when snowflakes are in the air, and it obscures all objects, whether light or dark in color.
Having stumbled across the entry for whiteout in the course of a regular review of meteorological terms, we immediately recognized that the existing definition, though well-attested and accurate, didn’t cover the most widespread use of the term. We therefore decided to add the new sense of whiteout, as part of our semiannual update of the dictionary.
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