From Bushwalk Australia
A weather phenomenon, where visibility is reduced to almost zero. It can be caused by a number of things including falling snow, particularly in blizzard conditions, low cloud, or accumulating fog and mist. White out conditions can be accompanied by rain and may be carried in by wind. In Tasmania it is common to see white outs occuring around the tops of mountains and other high places, rendering them invisible. It is dangerous to ascend or descend these places during a white out.