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CINDY DAY: Stepping outside the cloud chart

Stephanie spotted these mare's tails and mackerel scales high in the sky over Lunenburg County, N.S.
Stephanie spotted these mare's tails and mackerel scales high in the sky over Lunenburg County, N.S. - Contributed

The other day, Stephanie was strolling through another lovely new winery in Newburne, N.S., when she noticed delicate cloud filaments stretched across the midday sky. She tweeted the photo and I thought I would explain. 

On the cloud charts they are known as cirrus clouds. Cirrus clouds are high-level clouds and are generally characterized by thin, wispy strands. They form in the upper troposphere and because they are so high in the sky, they are made up entirely of ice crystals. Cirrus clouds can be almost invisible or milky looking and thick enough to partially obscure the sun. Cirrus is Latin and means ringlet or curling lock of hair.  

Grandma didn’t have a cloud chart but knew these clouds very well; she called them “mare’s tails.” Look again, that’s really what they look like.

I was out sailing on the weekend (more on that later) and while I didn’t think to ask, I’m sure most sailors would be familiar with the expression: “Mares’ tails and mackerel scales make tall ships take in their sails.”

So we’ve gone over the mare’s tails, but what about the mackerel scales? The strands of these cirrus clouds sometimes appear in tufts and when they do, they are categorized as cirrocumulus clouds – that happen to look an awful lot like the scales on a mackerel fish.

There, a “mackerel sky” is one that has a lot of cirrocumulus clouds. That type of cloud formation often precedes an approaching warm front.  Warm fronts often bring veering winds and precipitation.

Years ago – long before 24-hour weather networks, smart phones and weather apps – people who worked outdoors learned to read the signs of changing weather.  In so many cases it was essential to their livelihood and often times, their safety.  

So there you have it, another great observation that connects Nature’s beauty to science with a little detour to Grandma’s house.

Cindy Day is the chief meteorologist for SaltWire Network.

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