Ice fog  From Wikipedia, the free encyclopedia   (Redirected
from Pogonip) Jump to: navigation, search Ice fog over
Fairbanks, Alaska in winter 2005. Temperature approximately
minus 30F. Note the mirage at the base of the Alaska Range Ice
fog in Virginia City, Nevada, from an early 20th-century
postcard  Ice fog is a type of fog consisting of fine ice
crystals suspended in the air. It can happen only in cold areas
of the world since water can remain liquid down to −40 °C
(−40 °F). It should be distinguished from diamond dust, a
precipitation of sparse ice crystals falling from a clear
sky.[1]  In the United States[edit]  In the western United
States, ice fog may be referred to as pogonip.[2][3] It occurs
very rarely during cold winter spells, usually in deep mountain
valleys. Ice fog can be quite common in interior and northern
Alaska, since the temperature frequently drops below -40° in the
winter months. Pogonip only forms under specific conditions; the
humidity has to be near 100% as the air temperature dr