Pyrocumulonimbus

A large, intense fire heats nearby air, which rises while carrying water vapour, smoke and other particles. As the plume rises and cools, condensation can form a convective cloud. Under suitable atmospheric conditions, strong fire-driven convection develops into a pyrocumulonimbus, a thunderstorm-like cloud sometimes called a fire cloud. Its growth depends on both the fire and the surrounding atmosphere; not every wildfire produces one.

A mature pyroCb can act as a powerful vertical pathway for smoke and aerosols. Some events have injected material into the upper troposphere or lower stratosphere, where circulation can spread it far from the fire and allow it to remain aloft longer than smoke confined to the lower atmosphere. PyroCbs may produce lightning, hail, strong downdrafts and abrupt wind shifts. Lightning and wind changes can create additional dangers for nearby communities and firefighting operations, though the specific hazards vary by event.

Smoke particles affect sunlight and atmospheric chemistry. In a study of the 2017 Northern Hemisphere fire season, researchers used airborne measurements and particle characteristics to identify a substantial pyrocumulonimbus contribution to lower-stratospheric carbonaceous aerosol; NOAA's account of the work reports that the smoke was tracked by remote sensing for more than eight months. Such results show that the largest events can have effects beyond the immediate fire region. The sign and magnitude of climate effects depend on aerosol properties, altitude, sunlight and atmospheric conditions, so one event should not be treated as a simple measure of long-term climate impact.

PyroCbs are episodic and may evolve rapidly, making aircraft sampling difficult and leaving gaps in observations. Satellite measurements help detect cloud and smoke plumes, while research aircraft and atmospheric profiles can investigate their composition and vertical extent. A 2022 review summarized a worldwide event record for 2013–2021: although some years had high counts, the analyzed record did not support identifying a trend. The authors emphasized the need for broader, continuous records to understand regional and historical variability. Forecasting tools are being developed to identify environmental conditions that could favor pyroCb development, but reliable prediction remains challenging.