Incredibly rare cloud formations spotted looming over Vancouver

Blanketing 'asperitas clouds' filled the skies over Vancouver on Friday, Nov. 9. (Courtesy: Tiffany Mallen)

Weather watchers were treated to a unique display on Friday evening as rare cloud formations filled Vancouver skies.

The weather phenomenon cast sheets of grey-tinged cloud, knitted together to form an undulating pattern, across skies from North Vancouver to Port Moody throughout the evening.

The striking weather was a result of asperitas clouds, an exceptionally rare cloud formation that holds much mystery even for forecasters, said Environment and Climate Change Canada meteorologist Nan Lu.

"Unfortunately, we currently do not have a clear answer for their formation," said Lu.

Typically, they tend to appear before and after storms, and while little is known about why they occur the formations are believed to be associated with unstable atmospheres, she said.

Changing wind directions are likely the reason behind the wavy texture of the clouds, she added.

According to the Met Office, the first documentation of the cloud formation to the World Meteorological Organisation's International Cloud Atlas didn’t occur until 2008, when it was proposed by the Cloud Appreciation Society. The formation was officially recognised in 2015, when the classification was accepted at the WMO's 17th Congress.

Those who witnessed the phenomenon on Friday took to social media to share photos of evening skies resembling thick, rolling duvets or vast, choppy seas.

Given little is known about the haunting formations, Lu said it can be difficult to forecast the phenomenon, meaning those who are hoping to capture the scenes in future may have to rely on nothing more than sheer luck and a quality camera.