Pyrocumulus Clouds Fan the Flames - the Storm Systems of Wildfires

Summer is here in Canada, which means forest fire season is, too. Across the country, fire crews are battling flames that threaten homes, communities, forests, animals, and infrastructure (use this interactive map to see exactly where). The ones that rage out of control will be labeled ‘wildfires’. They stand out because they are bigger, spread faster, are unpredictable, and are hard to contain.

Wildfires can be incredibly destructive forces of nature, but there is some cool science at work! Did you know that wildfires can create their own cloud and storm systems? They can, and it’s all started off by the formation of pyrocumulus clouds.

As their alternative name, fire clouds, suggests, these clouds are created above heat sources - both natural and manmade. In latin, ‘pyro’ means fire, while cumulus means ‘heap’ or ‘pile’. This is a good description, as these cloud formations get very tall - as high as 30,000ft, the cruising altitude of commercial jets.

Billowing pyrocumulus clouds are most commonly associated with wildfires or volcanic eruptions. Their color can range from grey to brown due to the presence of ash and smoke within the cloud. As wildfires grow and become larger, strong, hot winds feed the flames the oxygen they need to continue burning and expanding to new sources of fuel.

To Make a Cloud System

You may notice that pyrocumulus clouds look like thunderheads - cumulonimbus clouds. In some ways, they act like them, too.

Wildfires create a lot of heat as they burn (1). As a result, the warming air at the surface of the earth begins to expand, becoming less dense, and then rising up high (2). This is called convection. Cooler air rushes in to take its place, creating strong, gusting winds (3). Moisture released from burned vegetation and found in the atmosphere condenses around particles of ash from the fire, causing pyrocumulus clouds to form (A). These clouds tend to expand because the ash particles inside of them pick up so much moisture.

Pyrocumulus cloud systems are known for severe turbulence, which occurs due to the winds created by the fire at the surface. Strong winds can drive the fire and make it worse as they continue to blow and feed the fire oxygen - just like when you fan the flames of your campfire. Winds can carry heat and embers from the fire ahead of the main blaze, causing it to spread faster. Sudden shifts in the direction of the wind make wildfires unpredictable and dangerous for fire crews fighting them on the ground.

The largest and most extreme form of these clouds are called pyrocumulonimbus clouds. Often, they are observed forming over volcanic eruptions. Pyrocumulonimbus clouds are even taller and more violent than pyrocumulus clouds, and produce dry lightning - an added complication. The dry lightning created by these systems is a danger because it can spark new fires in the surrounding areas, making the wildfire harder to contain.

Like the pyrocumulus variety, these storm systems create extreme winds that continue to make wildfires harder to fight, and generally make the situation worse. Winds can become so violent that they create tornadoes of fire, like this one caught on video in St. Albert, Alberta.

But don’t worry - there is some good news! While these massive cloud systems can hinder fire fighting efforts and fan the flames, there is potential for them to act as a helpful force. We know that pyrocumulus and pyrocumulonimbus clouds are full of condensed moisture. Sometimes the moisture present in the air and the cloud condenses enough that it begins to fall as rain, putting a damper on the very fire that created it. Each fire is unique, and so fire crews must respond to each on a case by case basis

Intrigued? You can learn more about wildfires and see crews battling a real blaze at the Wildfires in 4D Show!

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Jordan Nicksy is a graduate student in the Science Communication program at Science North & Laurentian University.