Editing Fog (section)

=== Freezing conditions ===
'''{{visible anchor|Freezing fog}}''' occurs when liquid fog droplets freeze to surfaces, forming white soft or hard [[rime ice]].<ref>{{cite web |url=https://w1.weather.gov/glossary/index.php?word=FOG |title=NWS Glossary |publisher=National Weather Service |date=2022}}</ref><ref name="bbcw" /> This is very common on mountain tops which are exposed to low clouds. It is equivalent to [[freezing rain]] and essentially the same as the ice that forms inside a freezer which is not of the "frostless" or "frost-free" type. The term "freezing fog" may also refer to fog where water vapor is [[Supercooling|super-cooled]], filling the air with small ice crystals similar to very light snow. It seems to make the fog "tangible", as if one could "grab a handful".
[[File:Aerial View of freezing fog in the Okanagan Highlands.webm|thumb|[[Aerial photography#Aerial video|Aerial video]] of freezing fog in the [[Okanagan Highlands]] ]]

In the [[western United States]], freezing fog may be referred to as '''pogonip'''.<ref name="merriam-webster">{{Cite Merriam-Webster|pogonip}}</ref> It occurs commonly during cold winter spells, usually in deep mountain valleys. The word pogonip is derived from the [[Shoshone]] word ''paγi̵nappi̵h'', which means "cloud".<ref name="merriam-webster" /><ref name="dictionary.com">{{cite web|url=http://dictionary.reference.com/browse/pogonip?s=t|title=Pogonip – Definition from the Dictionary.com|access-date=2013-01-02|url-status=live|archive-url=https://web.archive.org/web/20140222133643/http://dictionary.reference.com/browse/pogonip?s=t|archive-date=22 February 2014}}</ref>
In ''[[The Old Farmer's Almanac]],'' in the calendar for December, the phrase "Beware the Pogonip" regularly appears. In his anthology ''Smoke Bellew'', [[Jack London]] describes a pogonip which surrounded the main characters, killing one of them.

The phenomenon is common in the inland areas of the Pacific Northwest, with temperatures in the {{convert|10|to|30|°F|°C|abbr=on}} range. The [[Columbia Plateau]] experiences this phenomenon most years during [[temperature inversion]]s, sometimes lasting for as long as three weeks. The fog typically begins forming around the area of the [[Columbia River]] and expands, sometimes covering the land to distances as far away as [[La Pine, Oregon]], almost {{convert|150|mi|km}} due south of the river and into south central Washington.

'''Frozen fog''' (also known as '''ice fog''') is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally, this requires temperatures at or below {{convert|-35|°C|°F|abbr=on}}, making it common only in and near the [[Arctic]] and [[Antarctic]] regions.<ref>Haby, Jeff. [http://www.theweatherprediction.com/habyhints/359/ What is the difference between ice fog and freezing fog?] {{webarchive|url=https://web.archive.org/web/20060108091322/http://www.theweatherprediction.com/habyhints/359/ |date=8 January 2006 }} theweatherprediction.com</ref> It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. It can be associated with the [[diamond dust]] form of precipitation, in which very small crystals of ice form and slowly fall. This often occurs during blue sky conditions, which can cause many types of halos and other results of refraction of sunlight by the airborne crystals. Ice fog often leads to the visual phenomenon of [[light pillar]]s.

<gallery mode="packed">
File:PostcardVirginiaCityNVPogonipCirca1907.jpg|Pogonip fog in [[Virginia City, Nevada]], from an early 20th-century postcard
File:Tree in field during extreme cold with frozen fog.png|A tree in a field during extreme cold with frozen fog
File:Näsijärvi, Tampere, Finland. January 2019.jpg|Ice fog on [[Pyhäjärvi (Tampere region)|Pyhäjärvi]], [[Tampere]] during sunset.
</gallery>