Fire from fire: How wildfires can create their own weather and lightning

The recent wildfires in Alberta have included some pyrocumulus clouds. These clouds create their own local weather and even lightning that can ignite more fires. We look at how they form, and what we expect with lightning and climate change.

‘Canada is probably the corner of the world that gets the most pyrocumulonimbus’

A billowing cloud from a wildfire, taken at 38,000 feet.

The Prairies Climate Change Project is a joint initiative between CBC Edmonton and CBC Saskatchewan that focuses on weather and our changing climate. Meteorologist Christy Climenhaga brings her expert voice to the conversation to help explain weather phenomena and climate change and how they impact everyday life.

This spring's surge in expansive wildfires in Alberta have many thinking about how these fires get started.

We know that wildfires are generally caused by humans or lightning. But when conditions are right, some wildfires can create their own weather, including lightning strikes that can spark even more fires.

The 10-dollar word for this phenomenon is pyrocumulonimbus, which are thunderstorm clouds that form from the energy of a wildfire. Though they don't bring any rain, they do create weather that can aggravate an already critical fire situation.

So how do these impressive and dangerous fire clouds form? And what do they mean for firefighting efforts?

A helicopter flies near a large wildfire.

Fire storm formation

Pyrocumulonimbus clouds are formed from large and intense wildfires, and when weather conditions are hot, dry and windy. The heat from these fires drive the cloud formation.

"They're formed almost mysteriously from the fire," said Mike Fromm, a meteorologist with the Naval Research Lab in Washington, D.C.

The clouds begin as pyrocumulus clouds, which were spotted Friday within the wildfires in Alberta.

If they grow large enough, they begin to emulate thunderstorm clouds and are called pyrocumulonimbus clouds. Experts don't fully understand the trigger for this change, Fromm said.

"When the fire generates a certain amount of what we call a heat release … it passes some threshold, which is really not known," he said.

But when it does happen, the fire will change from being a horizontal "wind-driven" fire to more of a vertical plume, or what's called "a column-dominated fire," he said.

Challenges with suppression

The changes to local weather — particularly the wind — caused by these large fire clouds can be particularly hazardous to firefighters.

"If you are there trying to suppress the fire, you pretty much give up when it gets to this very intensive large level because the winds become stronger and they become more erratic," Fromm said.

Visibility can also become an issue with pyrocumulonimbus clouds, according to Fromm.

"It can truly turn mid-afternoon into nighttime conditions. So if you're up there close to the fire, trying to manage it or to manage evacuations, you have frightening conditions where it becomes very dark."

If the clouds are large enough, they can produce lightning but without the fire-quenching benefit of rainfall that you would usually see with thunderstorms.

A large pyrocumulus cloud as seen from the air over a B.C. wildfire.

"If it's striking an area of fuel that hasn't been lit, it can start a new fire," he said. That can be incredibly dangerous, potentially leaving crews dealing with fires on all sides.

Lightning and climate change

Fromm said that because of the unpredictability of these fire storms, more research is key.

It's especially critical here in Canada.

"Canada is probably the corner of the world that gets the most pyrocumulonimbus," he said.

"What we scientists would like to do is to go from hypothesis to prediction — and we're gaining some success in that."

And while the pyrocumulonimbus phenomenon is a newer area of study, researchers are also looking into broader trends involving lightning as our climate continues to change.

"In Canada, it's not a homogeneous picture, but there is evidence that lightning will increase at our latitudes," said Cynthia Whaley, a research scientist with Environment and Climate Change Canada.

Whaley said that if there are high levels of warming, we could see more lightning due to our hotter summers by the end of the century.

"It's definitely a result of convection," she said. "So the warmer the temperatures at the surface, the more convection you have. These updrafts create the lightning," she said.

And as fire seasons start earlier and last longer, Whaley said it is possible the likelihood of lightning-ignited fires — from both fire clouds thunderstorms — will increase, as will the size of the area that could be affected.

"You get lightning further north where you used to not see lightning," she said. "Like the Arctic."

Our planet is changing. So is our journalism. This story is part of a CBC News initiative entitled "Our Changing Planet" to show and explain the effects of climate change. Keep up with the latest news on our Climate and Environment page.

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