This fall, residents of Vancouver, B.C., and Ottawa, Ont., were lucky enough to witness an unusual, picturesque phenomena known as asperitas clouds. Resembling a churning sea on a stormy day, the clouds form when wind patterns speed up and clash high in the atmosphere, resulting in tension that creates a rippled texture in the fluffy floaters.
Though rare to folks who don’t normally notice clouds, retired Environment and Climate Change Canada meteorologist Phil Chadwick says asperitas can be seen at least a couple of times a year, depending on where you live. “In the city, you can’t see these phenomena very easily,” he said, “but they are dramatic and people have cell phones, so all of a sudden you’re seeing them everywhere.”
Chadwick says the pretty, serene clouds indicate turbulence and disruption higher up. “What’s happening in the atmosphere is very interesting. It’s a marginally unstable air mass filled with a lot of wind shear,” he says, referring to a change in wind speed over a short distance. “I’ve used the analogy of a giant walking across a taut bed sheet—it’s going to cause dimples. That’s kind of what we can see occurring with the asperitas cloud.”
Asperitas, which means “roughness” in Latin, were only added to the World Meteorological Association’s International Cloud Atlas in 2017. The cloud formation is said to have been first observed in Iowa in 2006. Though they typically form before or after storms, they don’t produce rain, and Chadwick says they often indicate a pleasant weather day with gentle wind.
While there’s no clear consensus on whether climate change is causing more asperitas appearances, Chadwick says that the conditions for their formation are becoming more common. For one, global warming has caused the atmosphere to hold about 10 per cent more moisture, meaning cloud formation in general is more likely.
There’s also the weakening jet stream, an air current that travels west to east globally and helps move different weather patterns. “Right now, it’s more like a meandering stream instead of a strong current of air, so things move slower,” Chadwick explains. This means we’re seeing prolonged periods of rain, drought, and other weather events. And yes, more chance for prolonged cloud cover, and thus potential for formations like asperitas.
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Chadwick says he hopes the excitement over asperitas and other unique cloud formations can translate into real appreciation for the environment. “I think, if you increase knowledge and awareness for people, they’re more likely to slow down their busy lives and appreciate nature and the world around them. Hopefully they realize this beauty and that we need to do something to conserve it as well,” he says.
For Chadwick, his appreciation of the natural world runs deep. In a recent blog post about asperitas, he wrote: “Clouds are the vocabulary of the weather with novel text freshly printed in the sky every day for all to read and appreciate.” It’s part of what inspires his practice of painting landscapes: he’s at two thousand and counting.
“The weather is always there for me,” he says. “And there’s always something interesting happening in the sky.”
Indeed there is. Don’t forget to look up, cottagers!
Editor’s note: An earlier version of this story incorrectly stated that the atmosphere’s jet stream moves east to west. The story has since been updated to reflect that the current moves west to east.
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