Mackerel sky

{{short description|Clouds displaying an undulating, rippling pattern look like fish scales}}

{{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)
-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;{{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}}{{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}} this is caused by high altitude atmospheric waves.{{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}}

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. 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.{{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}} The old rhymes "Mackerel sky, not twenty-four hours dry" and "Mares' tails and mackerel scales make lofty ships to carry low sails"{{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 }} both refer to this long-recognized phenomenon.

File:NorwegianMackerelatZionMarketSanDiegoCA.jpg

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".{{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}}

It is sometimes known as a buttermilk sky, particularly when in the early cirrocumulus stage, in reference to the clouds' "curdled" appearance.{{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}}