Mackerel sky

A mackerel sky is a common term for a sky with rows of cirrocumulus or altocumulus clouds displaying an undulating, rippling pattern similar in appearance to fish scales;[1][2] this is caused by high altitude atmospheric waves.[3]

Mackerel sky
Altocumulus mackerel sky
AbbreviationAc
Symbol
GenusAlto- (mediumhigh)
-cumulus (heaped)
AppearanceClumps and rolls of clouds that resemble mackerel scales
Precipitation cloud?No, but may signify approaching precipitation.

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.[4] 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 the warm front or low has moved closer and it may start raining within less than six hours.[5] The old rhymes "Mackerel sky, not twenty-four hours dry"[3] and "Mares' tails and mackerel scales make lofty ships to carry low sails"[6] both refer to this long-recognized phenomenon.

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".[4]

It is sometimes known as a buttermilk sky, particularly when in the early cirrocumulus stage, in reference to the clouds' "curdled" appearance.[7] In France it is sometimes called a ciel moutonné (fleecy sky); and in Spain a cielo empedrado (cobbled sky);[8] in Germany it is known as Schäfchenwolken (sheep clouds), and in Italy the clouds are described as a pecorelle (like little sheep).

In culture

Peter Paul Rubens' A View of Het Steen in the Early Morning (c.1636) features the first convincing 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.

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References
  1. Downing, L. L. (2013). Metereology of Clouds. p. 154.
  2. Ahrens, C. Donald; Henson, Robert (2015). Metereology Today. Cengage Learning. p. 153.
  3. Wong, Chi-wai. "Mackerel sky, not twenty-four hours dry". Hong Kong Observatory.
  4. "Ontario Regional Marine Guide". Environment Canada. Archived from the original on 2015-12-03.
  5. "Mackerel sky". Weather Online. Retrieved 21 November 2013.
  6. "Making heads of mares' tails". NASA Earth Data.
  7. Klocek, Dennis (2010). Climate: Soul of the Earth. SteinerBooks. p. 32.
  8. Hamblyn, Richard (2011). The Invention of Clouds: How an Amateur Meteorologist Forged the Language of the Skies. Pan Macmillan. p. 240.



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