Once the storm passed, residents near Regina were treated to a dramatic display as the prairie sky filled with lobe-like clouds. The unusual occurrence spawned a flurry of images on social media showcasing the oddly shaped formations.
CBC meteorologists Claire Martin and Johanna Wagstaffe say the weather conditions over Saskatchewan created a kind of perfect storm for mammatus cloud formation.
“Basically, when air that is full of big water droplets gets carried up to the top of a thunderstorm cloud, some of the air spreads out along the anvil shape at the very top,” says Wagstaffe.
The air at that altitude is cold enough to freeze the water droplets and the resulting crystals sink back down towards Earth, collecting at the base of the cloud.
Normally water droplets below the anvil part of the cloud evaporate quickly, contributing to a storm cloud's flat shape.
With mammatus clouds, Wagstaffe says, “the newly formed ice crystals need more energy to evaporate so pouch-like structures form” as more and more ice-laden air collects before it all has time to evaporate.
It’s this heavy, moisture-laden air that creates the shapes that inspire their name.
“Mammatocumulus, or mammary clouds got their name because they resemble udders, or whatever else your imagination brings you to,” says Wagstaffe.
While most clouds have wispy edges, mammatus lobes, usually only stable for a few minutes, form well-established boundaries that result in the dense, rounded shapes seen over Saskatchewan on June 26. The storm over Saskatchewan was a “classic example of a rotating storm,” says Martin.
Days of unseasonably warm weather preceding the advance of a cold front created “the potential for spin in the upper atmosphere," Martin says. The low pressure associated with the storm put “virtually everything in place for some nasty rotating storms.”
Whenever a storm is set up that way, “mammatus clouds are virtually always present,” says Martin.