Why that huge smoke plume wafted over Calgary Wednesday
Unusual phenomenon saw high-altitude streak blot out the sun but leave air quality relatively unaffected
Have you been wondering about that huge smoke plume that wafted over Calgary Wednesday?
So have we.
So we asked some experts about the unusual phenomenon, which saw a streak of thick smoke rapidly approach from the west and blot out the sun Wednesday afternoon.
The plume remained at high altitudes, leaving air quality at ground level relatively unaffected, and while it spread slightly out as it moved eastward, it kept a distinct shape.
Here's what it looked like from space.
(Imagery via Colorado State University's Regional and Mesoscale Meteorology Branch)
As you can see from the animation above, the smoke originated from a point in the Rockies.
That point was the Verdant Creek wildfire, the one that's been burning in Kootenay National Park, just a couple of kilometres west of Banff's Sunshine Village resort.
The fire had been largely contained but it suddenly flared up again Wednesday, in spectacular fashion, shooting a mushroom-shaped cloud high into the sky.
Here's what it looked like from Tent Ridge in Kananaskis country.
That massive eruption of rapidly rising smoke is due to the intense heat of the wildfire, said Torah Kachur, the syndicated science columnist for CBC Radio One.
"A forest fire creates a lot of ground heat and that heat rises — in some cases rises rapidly — if there's a large difference in temperature between the ground and air," she explained.
"Then when it contacts the jet stream — in particular in Calgary, and if that jet stream is low — then that change in temperature causes water to condense on the ash and soot from the fire, causing a cloud."
In some cases, these types of clouds, known as flammagenitus or pyrocumulus clouds, can even create their own lightning.
"This was seen last year in Fort Mac but so far has not been reported for the B.C. fires," Kachur said.
As the smoke plume drifted eastward toward Calgary, its imposing mass became apparent to people in the city.
But while Calgarians have become accustomed to smoky air from the British Columbia wildfires in the past few weeks, this plume didn't make its way down to ground level.
"That plume came right across the Rockies and sort of fumigated the upper atmosphere over top of Calgary and didn't broaden out that much until it got past Calgary," said Brian Proctor, a meteorologist with Environment Canada.
"What perhaps was most interesting was that it chose to mainly stay aloft."
That behaviour of the plume "requires a combination of factors," Proctor added.
In this case, the flare-up of the wildfire was hot enough to throw the smoke exceptionally high into the atmosphere and then the atmosphere happened to be quite stable that day, keeping the smoke aloft and relatively contained in a tight plume.
"Calgary, itself, was really at the end of the fire hose of smoke that was coming across from Kootenay National Park," Proctor said.
A large column of smoke from the Verdant Creek wildfire may be visible in the Bow Valley and Columbia Valley over the next few days, as well as along highways in the Rocky Mountains, according to Parks Canada.
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