A fire whirl (or fire tornado) forms when the intense heat of a fire generates a rising air column that acquires rotation. The weakest are small flame vortices a few metres across; the most extreme can be genuine tornadoes with winds exceeding 200 km/h.
Mechanism
The fire heats the air intensely, creating powerful updrafts. If ambient wind shear exists or terrain channels the flow, the column can spin. In extreme cases, such as the Canberra fires (2003) and California's Carr Fire (2018), EF-3 fire tornadoes devastated areas outside the original fire perimeter. Pyrocumulonimbus can intensify the phenomenon.