From Glossary of Meteorology
(Also called milky weather.) An atmospheric optical phenomenon in which the observer appears to be engulfed in a uniformly white glow.
Neither shadows, horizon, nor clouds are discernible; sense of depth and orientation is lost; only very dark, nearby objects can be seen. Whiteout occurs over an unbroken snow cover and beneath a uniformly overcast sky, when, with the aid of the snow blink effect, the light from the sky is about equal to that from the snow surface. Blowing snow may be an additional cause. This phenomenon is experienced in the air as well as on the ground.