A mackerel sky is a common term for clouds made up of rows of

cirrocumulus Cirrocumulus is one of the three main genus-types of high-altitude tropospheric clouds, the other two being cirrus and cirrostratus. They usually occur at an altitude of . Like lower-altitude cumuliform and stratocumuliform clouds, cirrocumulus ...

altocumulus Altocumulus (From Latin ''Altus'', "high", ''cumulus'', "heaped") is a middle-altitude cloud genus that belongs mainly to the ''stratocumuliform'' physical category characterized by globular masses or rolls in layers or patches, the individual ele ...

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

s displaying an undulating, rippling pattern similar in appearance to

fish scales A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

; this is caused by high altitude

atmospheric waves An atmospheric wave is a periodic disturbance in the fields of atmospheric variables (like surface pressure or geopotential height, temperature, or wind velocity) which may either propagate ('' traveling wave'') or not (''standing wave''). Atmosp ...

. Cirrocumulus appears almost exclusively with

cirrus Cirrus may refer to: Science *Cirrus (biology), any of various thin, thread-like structures on the body of an animal *Cirrus (botany), a tendril * Infrared cirrus, in astronomy, filamentary structures seen in infrared light *Cirrus cloud, a typ ...

some way ahead of a

warm front A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fr ...

and is a reliable forecaster that the weather is about to change. When these high clouds progressively invade the sky and the

barometric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibar ...

begins to fall,

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hai ...

associated with the disturbance is likely about 6 to 12 hours away. A thickening and lowering of cirrocumulus into middle-étage

altostratus Altostratus is a middle-altitude cloud genus made up of water droplets, ice crystals, or a mixture of the two. Altostratus clouds are formed when large masses of warm, moist air rise, causing water vapor to condense. Altostratus clouds are usuall ...

is a good sign that the warm front or low front has moved closer and it may start raining within less than six hours. The old rhymes "Mackerel sky, not twenty-four hours dry" and " Mares' tails and mackerel scales make lofty ships to carry low sails" both refer to this long-recognized phenomenon. Other phrases in

weather lore Weather lore is the body of informal folklore related to the prediction of the weather and its greater meaning. Much like regular folklore, weather lore is passed down through speech and writing from normal people without the use of external me ...

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". It is sometimes known as a buttermilk sky, particularly when in the early cirrocumulus stage, in reference to the clouds' "curdled" appearance. In France it is sometimes called a ''ciel moutonné'' ( fleecy sky); and in Spain a ''cielo empedrado'' ( cobbled sky); 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 Sir Peter Paul Rubens (; ; 28 June 1577 – 30 May 1640) was a Flemish artist and diplomat from the Duchy of Brabant in the Southern Netherlands (modern-day Belgium). He is considered the most influential artist of the Flemish Baroque tradit ...

' '' A View of Het Steen in the Early Morning'' (1636) features the first convincing depiction of a mackerel sky in art. " Ole Buttermilk Sky" by

Hoagy Carmichael Hoagland Howard Carmichael (November 22, 1899 – December 27, 1981) was an American musician, composer, songwriter, actor and lawyer. Carmichael was one of the most successful Tin Pan Alley songwriters of the 1930s, and was among the firs ...

was nominated for an Academy Award for Best Original Song in 1946.

Gallery

File:Mackerelskybig2.jpg, Mackerel sky over

Erlangen Erlangen (; East Franconian: ''Erlang'', Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 116,062 inhabi ...

, Germany File:Metung-Wharf-Pano,-Vic.jpg, Mackerel sky over Metung, Victoria, Australia File:Altocumulusmackarel.jpg, Mackerel sky over

Heidelberg Heidelberg (; Palatine German language, Palatine German: ''Heidlberg'') is a city in the States of Germany, German state of Baden-Württemberg, situated on the river Neckar in south-west Germany. As of the 2016 census, its population was 159,914 ...

, Germany File:Peter Paul Rubens - A View of Het Steen 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.

References

External links

Cumulus {{Climate-stub