By Erik Baard
Recently I ran up the darkened stairs of the E train World Trade Center subway station. When the bright sun hit my squinting eyes at street level I thought, “Uh oh. It might rain on the EarthFair.”
The source of my concern was the southwestern sky, gently dappled with small white clouds in neat rows. Nothing could look more peaceable, but as a kayaker I’d absorbed the sailors’ lore of a “mackerel sky.” The festivities outside of Grand Central didn’t get rained out, but by Sunday it was touched-and-go during the cooler day and showers fell at night. Thanks to that bright Friday alert, however, I was prepared with waterproof bike pants and a jacket in my backpack.
A mackerel sky (as photographed above over the Upper West Side by Elizabeth Powers – click to enlarge) satisfies something inside me in a way that the Big Dipper does for casual stargazers. It’s a familiar touchstone that is unfailingly clear and bears a comfortably homey name.
“What you’re seeing is instability at an altitude of about 20,000-to-30,000 feet. It’s a disturbance that could, but not necessarily, lead to a cyclone. Or in other words, a storm,” said SUNY Stony Brook Institute for Terrestrial and Planetary Atmospheres meteorologist Brian Colle. “Those are cirrocumulus clouds that would look like little puffs to a pilot flying over them, but to us on the ground they look like scales.”
The less nautical Germans have traditionally called such views “sheep skies,” seeing rolls of wool where the British saw a King Mackerel, as photographed below for a Smithsonian field guide to bony fishes (click to enlarge). Sometimes the rows of cloud “scales” can be arranged in stunning arcs, with blue stripes separating them.
But how reliable is it as a forecasting tool? Common belief is that two critical factors are whether there’s much moisture at lower altitudes and if surface temperatures are unstable, as they often are in this region of ocean and land interaction, and urban heat islands. When they grow larger, it’s said that cooler weather is coming, perhaps with larger thunderstorms.
The rule of thumb I inherited from old salts since artist and outdoorsman Steve Sanford first taught me about mackerel skies is that rain is 70% likely within two days of a sighting. Colle puts that at “maybe a 50% chance of rain within 24 hours. Is that reliable? Not very, compared to the computers and instruments we have today.”
Colle, who researches North American coastal meteorology, compares the old saw about mackerel skies (“Mackerel sky, mackerel sky. Never long wet, never long dry.”) to that of “Red sky at night, sailor’s delight. Red sky in morning, sailor take warning.” He credits 18th century mariners, crews from the height of the golden age of sail, with such observations, though this folk wisdom certainly has deeper roots in time. Consider, however, that the naked eye viewing range limited to about 10 miles and a sailor’s noggin lacks the processing power of parallel processing supercomputers.
“They were useful pattern recognitions before we had computers,” Colle said. “The good news is that we understand more of the physics of the problem. We have computers, instruments, and formulas that can predict weather a lot more accurately than looking at clouds. We don’t even need to look at clouds anymore.”
Yet some of us still look. And perhaps even need to.
“I got interested in clouds is because of my work on the German writer Goethe, who wrote a series of poems inspired by Luke Howard’s cloud classifications,” explained Powers, an avid cloud photographer and Goethe scholar. She noted that in 1817, Goethe included this “sheep sky” verse in a piece praising Howard’s work.
And higher, higher yet the vapors roll:
Triumph is the noblest impulse of the soul!
Then like a lamb whose silvery robes are shed,
The fleecy piles dissolved in dew drops spread;
Or gently waft to the realms of rest,
Find a sweet welcome in the Father’s breast.
Whew! It takes a guy like Goethe to exalt the clouds themselves even higher!