{{short description|Clouds displaying an undulating, rippling pattern as that of mackerel skin}} {{redir|Buttermilk sky|the goat|Buttermilk Sky}} {{Infobox Cloud | name = Mackerel sky | image location = Mackerelskylincolnshire.jpg | image name = Altocumulus mackerel sky | abbreviation = Ac | symbol = Clouds CM 8.svg | genus= Alto- (''mediumhigh'')<br />-cumulus (''heaped'') | species= | variety= | altitude_m = | altitude_ft = | level = high to medium | appearance = Clumps and rolls of clouds that resemble mackerel scales | precipitation = No, but may signify approaching precipitation. }}
A '''mackerel sky''' is a term for clouds made up of rows of cirrocumulus or altocumulus clouds displaying an undulating, rippling pattern similar in appearance to fish scales;<ref>{{cite book|url=https://books.google.com/books?id=iazUAAAAQBAJ&pg=PT154|page=154|title=Metereology of Clouds|author=Downing, L. L.|year=2013|isbn=9781491804339}}</ref><ref>{{cite book|title=Metereology Today|url=https://books.google.com/books?id=5Dx-BAAAQBAJ&pg=PT153|first1=C. Donald |last1=Ahrens|first2= Robert|last2= Henson|year=2015|publisher=Cengage Learning|page=153|isbn = 9781305480629}}</ref> this is caused by high altitude atmospheric waves.<ref name="HKO">{{cite web|url=http://www.hko.gov.hk/education/edu01met/wxobs/folklore/ele_mackerel_e.htm|title=Mackerel sky, not twenty-four hours dry|author= Wong, Chi-wai|publisher=Hong Kong Observatory}}</ref>
Cirrocumulus appears almost exclusively with cirrus some way ahead of a warm front and is a reliable forecaster that the weather is about to change.<ref name="canada" /> When these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 12 hours away. A thickening and lowering of cirrocumulus into middle-étage altostratus or altocumulus is a good sign that the warm front or low front has moved closer and it may start raining within less than six hours.<ref name="Mackerel sky">{{cite web|url=http://www.weatheronline.co.uk/reports/wxfacts/Sometimes-a-bit-fishy.htm|title=Mackerel sky|publisher=Weather Online|accessdate=21 November 2013}}</ref> The old rhymes "Mackerel sky, not twenty-four hours dry"<ref name="HKO" /> and "Mares' tails and mackerel scales make lofty ships to carry low sails"<ref>{{cite web|url=https://earthdata.nasa.gov/user-resources/sensing-our-planet/making-heads-of-mares-tails|title=Making heads of mares' tails|date=11 October 2013 |publisher=NASA Earth Data|last1=Lefevre |first1=Karla }}</ref> both refer to this long-recognized phenomenon. thumb|Norwegian Mackerel displaying the skin pattern of a mackerel sky
Other phrases in weather lore take mackerel skies as a sign of changeable weather. Examples include "Mackerel sky, mackerel sky. Never long wet and never long dry", and "A dappled sky, like a painted woman, soon changes its face".<ref name="canada">{{cite web|url=https://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=928EE83A-1|title=Ontario Regional Marine Guide|publisher=Environment Canada|url-status=dead|archiveurl=https://web.archive.org/web/20151203133407/https://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=928EE83A-1|archivedate=2015-12-03}}</ref>
It is sometimes known as a '''buttermilk sky''', particularly when in the early cirrocumulus stage, in reference to the clouds' "curdled" appearance.<ref>{{cite book|url=https://books.google.com/books?id=n1s79da7DNUC&pg=PT32|page=32|title=Climate: Soul of the Earth |author=Klocek, Dennis|year=2010|publisher=SteinerBooks|isbn=9781584204589}}</ref>
==In culture==
Peter Paul Rubens' ''A View of Het Steen in the Early Morning'' ({{circa}}1636) features a depiction of a mackerel sky in art.
"Ole Buttermilk Sky" by Hoagy Carmichael was nominated for an Academy Award for Best Original Song in 1946.
==Gallery== <gallery class="center" widths="200" heights="200"> File:Mackerelskybig2.jpg|Mackerel sky over Erlangen, Germany File:Metung-Wharf-Pano,-Vic.jpg|Mackerel sky over Metung, Victoria, Australia File:Altocumulusmackarel.jpg|Mackerel sky over Heidelberg, Germany File:Peter Paul Rubens - View of Het Steen Castle in the Early Morning.jpg|Rubens' ''A View of Het Steen in the Early Morning'' File:Altocumulous clouds.jpg|Altocumulus mackerel sky clouds over Burlington, Canada. </gallery>
== See also == * {{Portal inline|Weather}}
==References== {{reflist}}
==External links== * {{Wiktionary inline}}
{{Cloud types}}
Category:Cumulus