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Spokane, Washington  Est. May 19, 1883
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Weathercatch: There’s something fishy in those clouds

This mackerel sky, made up of altocumulus cloudlets, was photographed at sunset on March 25 along a rural road in Whitman County.  (Photo courtesy of Ann Larsen Porteous)
This mackerel sky, made up of altocumulus cloudlets, was photographed at sunset on March 25 along a rural road in Whitman County. (Photo courtesy of Ann Larsen Porteous)
By Nic Loyd and Linda Weiford For The Spokesman-Review

Clouds have delivered plenty of trouble this spring – gloominess, downpours, late snowfalls and even two tornadoes. Furthermore, they’ve mostly obscured the warming sun. So we don’t blame you for being apprehensive about casting your eyes toward the sky.

But if you read our column regularly, you know that we look for silver linings in the ever-changing world of clouds. For every dark, dreary day, there’s a morning, afternoon or evening when the atmosphere puts on an art show for free.

Which brings us to a mackerel sky, a term for ripples of clouds that resemble fish scales. They occasionally make appearances in the Inland Northwest and it’s a beautiful sight, especially during sunset, as you can see from the photograph taken on March 25 in Whitman County.

A mackerel sky is made up of rows of either mid-level altocumulus or high-level cirrocumulus clouds that form in small clumps called cloudlets. Cirrocumulus cloudlets are formed very high in the atmosphere, so they typically appear grainy and wispy from a distance. In contrast, altocumulus cloudlets appear fuller and slightly larger since they’re closer to Earth.

Whether formed by cirrocumulus or altocumulus clouds, the result is a unique, somewhat orderly rippling pattern as if Mother Nature herself took a paintbrush to the sky. Mackerel sky is the common English term for this meteorological phenomenon, while in France it’s called ciel moutonne, or fleecy sky; and in Italy it’s pecorelle, like little sheep. The Cloud Appreciation Society describes it as a “sky of a thousand cloudlets.”

The unique formation is created when winds and gravity merge to create waves in the upper atmosphere. Oftentimes, a pattern of cirrocumulus cloudlets form ahead of an incoming weather change that may include precipitation. Back when sailors made weather forecasts based on the sky’s appearance, nautical weather sayings were born. Among them? “A mackerel sky denotes fair weather for that day, but rain a day or two after,” according to “Weather Lore: A Collection of Proverbs, Sayings and Rules,” published in 1898.

By the way, the cloudlets featured in the photograph are altocumulus. As you can see, the reflecting light of the sunset cast the clouds in stunning hues of silver, lavender and blue. Although mackerel skies aren’t rare, they can be hard to spot because the cloudlets typically drift away or dissipate fairly quickly.

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