A massive cloud — so large the plume is visible from space — continues to unfurl over the horizon of Fort McMurray, as a wildfire works its destruction on thousands of homes.

The ash-blackened sky cracked open with forks of lightning on Wednesday night, as the blaze expanded from 10,000 hectares to a devastating 85,000.

The wildfire threatening to engulf the city has become so powerful it has created its own firestorm.

Large wildfires can create wicked winds

Brian Proctor, a warning preparedness meteorologist for Environment Canada, says when fires get big enough, they begin to create weather systems of their own.

These firestorms are a powerful force. They can alter weather patterns, funnel smoke and particulates high into the stratosphere, and produce powerful lightning strikes.

"They tend to promote their own kind of conditions," Proctor said.

"That's why you'll see the winds near fires ... that are significantly stronger that the surrounding atmosphere."

These fire clouds, which can also form after massive explosions or volcanic eruptions, are formed when intense heat induces convection, which causes the air mass to rise rapidly.

Extreme wildfire in Fort McMurray area that's burned ~19,000 acres is seen by our satellites <a href="https://t.co/cW5rWrBGzt">https://t.co/cW5rWrBGzt</a> <a href="https://t.co/C4IZ0wUvBy">pic.twitter.com/C4IZ0wUvBy</a> —@NASA The intense, rising smoke and heat of a fire can cause storm clouds to form. These clouds are typically bigger, taller and darker than normal thunderstorm clouds.

"For example, if you're in your backyard with a fire pit, and you having the fire going, above that fire, you're heating the air significantly, and it's lifting up into the atmosphere quite rapidly, something has to come in to to replace that," Proctor said.

The turbulence in the atmosphere causes lightning strikes, but no rain. It's these conditions which can trigger another blaze.

These dirty storm clouds don't drift like normal weather systems. And, with the stagnant weather conditions caused by a low pressure system, the firestorm becomes tethered in place.

"That's one of the real problems and forecast situations for our partners who are doing the forecast meteorology for this storm," Proctor said.

"It's almost a self-perpetuating situation."

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