How Do Wildfires Create Their Own Thunderstorms?

Some wildfires become powerful enough to create their own weather. The heat pushes air, smoke and moisture upward so rapidly that a towering thunderstorm cloud can form above the fire.

This phenomenon is called a pyrocumulonimbus cloud. It can generate lightning, violent downdrafts and shifting winds, while carrying smoke far above the ordinary weather layer.

What is a pyrocumulonimbus cloud?

A pyrocumulonimbus cloud is a thunderstorm produced by intense heat from a wildfire or, less commonly, a volcanic eruption. Meteorologists often shorten the name to pyroCb.

It resembles an ordinary cumulonimbus cloud, but the initial upward motion is driven by fire rather than by daytime heating alone.

How does a wildfire build a thunderstorm?

A large fire heats the air near the surface. That air becomes buoyant and rises, carrying smoke, ash and water vapour with it.

As the plume climbs, the air cools. Water vapour can condense into droplets and ice, releasing additional heat that strengthens the upward motion. If the atmosphere is unstable enough, the plume can grow into a full thunderstorm.

Why can these clouds make a fire more dangerous?

The cloud can produce lightning that starts new fires beyond the original burn area. It can also create strong downdrafts and sudden wind shifts that spread flames in unexpected directions.

For firefighters, the greatest danger is rapid change. Conditions near the ground can deteriorate even when the cloud itself is kilometres above the fire.

How high can the smoke travel?

Strong events can push smoke through the troposphere and into the stratosphere. Smoke at that altitude may remain in the atmosphere much longer than smoke confined to lower layers.

It can then travel across continents and influence atmospheric chemistry, air quality and, in unusually large events, climate-related measurements.

How do scientists study fire-generated storms?

Researchers combine instrumented aircraft, weather radar, satellites, balloons, ground sensors and atmospheric models. Aircraft can measure particles, gases, temperature, humidity and winds inside or near the plume.

Satellites provide the broader view, showing how the smoke expands and moves after the storm forms. Ground instruments help connect conditions near the fire to what happens higher in the atmosphere.

Why are these storms difficult to predict?

The outcome depends on several interacting factors: fire intensity, available fuel, terrain, moisture, wind and the stability of the atmosphere. A fire may produce a large smoke column without developing into a thunderstorm.

Small changes can matter. A shift in wind or humidity may strengthen the plume, weaken it or move it away from the conditions needed for storm development.

Can climate change make these events more common?

Hotter and drier conditions can increase the likelihood of severe wildfires in many regions, which creates more opportunities for powerful smoke plumes. However, the formation of a pyrocumulonimbus cloud also requires suitable atmospheric conditions.

Scientists therefore avoid treating every rise in wildfire activity as a direct one-to-one increase in fire-generated thunderstorms. The relationship varies by region and weather pattern.

What are researchers trying to improve?

Researchers want better warning tools that can identify when a fire is approaching the threshold for generating a thunderstorm. They also want more accurate estimates of how much smoke reaches the stratosphere.

Better observations can improve fire behaviour forecasts, aviation warnings, air-quality models and understanding of the climate effects of extreme wildfire smoke.