Also known as fire whirls, fire devils, or even firenados, fire tornadoes form when high heat and turbulent winds together spur whirling eddies of air, mechanical engineer Jason Forthofer told National Geographic News in September.
These eddies can tighten into a tornado-like structure that sucks in burning debris and flammable gases, said Forthofer, of the U.S. Forest Service’s Missoula Fire Sciences Laboratory in Montana.
The fiery core inside the swirling “tube” of winds is usually about 1 to 3 feet (0.3 to 0.9 meter) wide and five to ten stories tall. At the extreme, though, fire tornadoes can stretch dozens of feet wide and more than a hundred stories tall, Forthofer said.
The firenadoes, he added, aren’t so much rare as rarely reported—perhaps because they tend to occur during wildfires, rather than in urban centers. | source