Wildfire-spawned thunderclouds: How fire-induced clouds are creating their own weather

Do you remember the blood-red skies over Australia in the wake of the 2019-2020 new year fires? The raging wildfires produced post-apocalyptic, Mad Max-esque skylines and looming columns of smoke, dubbing this period the “Black Summer.” 

These bushfires caused the formation of pyrocumulonimbus clouds (pyroCbs), coined “fire clouds.” This is a fire-atmosphere phenomenon caused by rising smoke, ash, and hot air from the original fires. 

These fire-induced clouds create a positive-feedback loop by creating their own weather patterns, spreading flames and ash over land like a parasitic animal desperate to find a new host.

What are pyrocumulonimbus clouds?

Picture a cloud of ash and smoke, billowing up far into the atmosphere. You may be recalling mushrooming smoke plumes towering above the ground, the kind often associated with a volcanic eruption or a nuclear bomb blast. There is a third major event that can cause this: wildfires. 

The intense heat released from wildfires causes the surrounding air to become hot. Hot air is less dense than cool air, and is forced upward, casting a super-heated updraft into a vertical column that rises higher as the air around it cools with elevation. The moisture in the hot air condenses at high altitudes, causing pyroCbs to form. 

“In the absence of their rain-making ability, PyroCbs create their own weather in three main ways: lightning, erratic winds, and fire vortexes.”

These clouds, however, are not the harmless pearly-white clouds of children’s storybooks. They are dark and spiraling thunderstorm-like cloud formations filled with smoke, ash, moisture, and other burning materials that loom over their parent wildfires. These clouds perform like thunderclouds, minus one key feature — their ability to form rain. 

PyroCbs can create wind and lightning, initiating their own weather patterns. However, due to the particulate matter and heat in the smoke, the clouds often lack the ability to produce precipitation, and consequently, rainfall. 

How do pyrocumulus clouds create their own weather?

It was long believed that pyroCbs could not move past the troposphere (the lowest level of the atmosphere) due to a lack of energy. Meteorologists at the US Navy, however, have proven that pyroCbs can indeed send smoke into the stratosphere (the second level of the atmosphere), making them more akin to a volcanic eruption. The billowing smoke injected into the stratosphere can persist upwards of a year and alter its composition and weather patterns.

Without precipitation, pyroCbs create their own weather in three main ways: lightning, erratic winds, and fire vortexes. 

As the moisture in the pyroCbs rises high into the atmosphere, it freezes, causing particle collisions that lead to a charge buildup. To neutralize this buildup, lightning occurs. Lightning without rain is known as dry lightning, which can be devastating for the land below as sparks can initiate new fires. 

PyroCbs can create their own erratic wind patterns as a result of the downdraft from the thunderstorm when it dies down. The winds from these clouds can carry sparks and embers far from the initial fire, causing new spot fires. 

PyroCbs can also stretch the air within its column, creating a vortex with tornado-strength winds, as the air in the cloud comes in contact with different wind speeds and directions.   

Looking forward

PyroCbs caused by wildfires cause unique weather patterns, spreading fires and making them harder to extinguish. This phenomenon has been exacerbated by climate change, as the intensity and prevalence of wildfires increase. In 2021, a fire in British Columbia spawned 700,000 lightning strikes, which is more than the average for an entire year. A different fire in B.C. in 2017 resulted in five pyroCbs in a singular day, pumping over 220,000 tons of smoke down to the lower stratosphere over only five hours.

There is rising alarm about the scale of pyroCbs, considering that they can breach into the stratosphere. The pollution generated from pyroCbs becomes a global phenomenon when they reach this level. As wildfires continue to escalate in frequency and scope, leading to larger and longer-lasting pyroCbs, the need for more research into these fire-born clouds grows.