Published on July 28, 2026
Pyrocumulonimbus clouds (pyroCb), or "fire clouds," form above large wildfires. The heat drives hot air, smoke and particles up into the upper troposphere, sometimes the lower stratosphere — above 10 km, where the vapor condenses into a genuine thunderstorm cloud, complete with lightning and winds.
What makes these clouds remarkable
→ It's not the size of the fire that decides, but the atmosphere. High temperatures, very dry air and strong instability aloft are the determining conditions.
→ One quiet indicator plays a central role: the vapor pressure deficit (VPD), a measure of how "thirsty" the air is. Its measurable rise is linked to warming.
→ The phenomenon is becoming more frequent. A worldwide inventory covering 2013 to 2023 shows a marked increase in events, with 2023 setting records.
Open questions
The consensus on the trend is solid. But the exact share of each atmospheric factor remains debated, as does the ability of models to predict when and where a fire will tip into a pyrocumulonimbus. That is precisely the focus of current research: better forecasting to better protect people and firefighters.
Sources
- Jain et al. (2021).
- Richardson et al. (2022).
- Peterson et al. (2025).
Want to explore a scientific topic that interests you? Try Scinuance AI for free, no account needed.
Try Scinuance AI →📄 Associated Scinuance Report
Access the full report on pyrocumulonimbus and wildfires: complete scientific sources, bibliography analysis, and synthesis of uncertainties.
View the full report →