Pyrocumulus clouds form under special conditions of extreme ground-level heat. In the sky they often resemble huge, brown or grayish brown, lumpy-surfaced puffballs. Pyrocumulus clouds originate most commonly in areas subject to frequent wildfires. These characteristic phenomena gave rise to the formation’s name, pyro being the Latin word for fire (pyromaniac, pyrotechnics), and cumulus for heap or “piled up.” The dense, dark coloration of pyrocumulus clouds give them a deservedly ominous cast.
When a wildfire churns through a dry tundra, sweeps across a plain of thick, parched grass or roars through a dense, dry woodland area, the intense heat of the fire causes the resulting smoke and ash to rise rapidly heavenward where it forms towering pyrocumulus clouds. Volcanic eruptions also give rise to fire clouds, the heated gases and ash billowing high over the volcanic cone or mountain. Another cause of pyrocumulus formations, nuclear explosions, present the too familiar mushroom clouds associated with atomic and hydrogen bomb testing. The connective factor in these events are the same: the generation of high heat continuing over a relatively long period of time. Depending on the intensity and duration of the fire and on atmospheric conditions, pyrocumulus clouds can reach to altitudes as high as 30,000 feet.
As the dense smoke- and ash-filled clouds reach higher and higher into the skies, the heated mass may contact moisture in the stratosphere or carry water released from the burning material with it. The formation may more and more begin to resemble a huge thundercloud. In fact, the rising plume of heated air and ash, upon contacting the cooler air, may begin to develop precipitation. With luck, the falling rain will have a restraining effect on the flames below (though probably not very much on the furnace of an erupting volcano).
On the minus side, certain conditions may develop in a pyrocumulus formation, especially one associated with volcanic activity, that will generate lightning. Around a volcanic cone, lightning strikes could cause fires to erupt where none had started. If the thunderclouds release lightning where a wildfire already exists, the blaze may become a veritable firestorm with this additional stimulus. High ground-level winds that more often than not occur in firestorm conditions make it extremely difficult for fire fighters as they risk their lives to quell a conflagration.
You may never see one of these magnificent, if terrifying, cloud formations. They primarily occur in areas that commonly suffer long periods of drought accompanied by lightning (or other) causes of wildfire. These contributory conditions exist in areas similar to southeastern Australia and California.