Bushfires are strongly driven by weather: hot, dry and windy conditions can combine to create the perfect environment for flames to spread across the landscape.

But sometimes the relationship flips: fires can generate their own weather systems, which can then dramatically alter the spread and intensity of the blaze.

One of the most striking examples of this phenomenon is the formation of pyrocumulonimbus clouds — towering storm clouds born from fire.

Large bushfires release enormous amounts of energy – sometimes comparable to that emitted from a nuclear bomb. This heats the air in the vicinity of the fire, causing it to rise rapidly in a powerful, buoyant, fire-driven updraft.

Surrounding air rushes in at ground level to replace the rising hot air, feeding the fire with oxygen like a bellows and sometimes accelerating its spread. In extreme cases, the fire and its induced winds can become a self-sustaining system, feeding and growing from the weather it creates.

If the plume rises high enough it can cool to a temperature where the water vapour in the plume will begin to condense into clouds. This is essentially the same process that leads to the formation of ordinary cumulus clouds, except it occurs within a fire’s plume and is called pyrocumulus.

If the fire is large and intense enough, the plume can keep rising. As the cloud rises above altitudes of around 3–5 kilometres, temperatures can drop well below freezing. Water droplets freeze into ice crystals, releasing another burst of latent heat that further energises the rising plume.

The rapidly rising plume now contains ice and supercooled water — a mixture that is key........

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