Pogonip is a Native American word for ice fog, which means white death.
Ice fog is fog composed of tiny frozen crystals of ice, causing it to shimmer. Ice fog requires bitter cold temperatures. It's a rare phenomenon unless you live up near the Arctic or Antarctic regions, such as in northern Alaska.
Unlike liquid in contact with surfaces, liquid precipitation, whether falling as rain or suspended in a cloud, can remain liquid in well below freezing temperatures. In fact, only at negative forty degrees will all suspended liquid freeze into ice.
Fog is generally created by moisture evaporating from the Earth's surface. As this moisture rises, it cools and condenses into what is, in effect, a cloud. Moist air traveling horizontally can also contribute to ice fog. In addition, in circumstances where warm air lies atop cold air, it can trap the evaporating moisture close to the earth's surface, causing ice fog as well. Finally, a good ice fog requires a little bit of a breeze to stir the air and really make the ice shimmer and sparkle.