They start from the smoky tendrils of wildfires trailing into the atmosphere. Forming first as small, white clumps of clouds, in as little as 30 minutes they can become imposing thunderstorms.

“It’s hard to overstate how dark they become,” says Nicholas McCarthy, a wildfire scientist at the University of Queensland in Australia, of the pyrocumulonimbus clouds that grow from intense wildfires.

Called pyroCbs for short, or often just fire storms, the dangerous atmospheric phenomena can worsen fires by generating intense winds, transporting embers, and striking lightning in yet- untouched regions.

During California’s infamous Carr fire in 2018, pyroCbs grew from three to seven miles across in just 15 minutes and spawned a fiery tornado. These fire storms have been seen in places