Fire whirls

A fire whirl – also commonly known as a fire devil, or, (in many cases) erroneously, as a fire tornado, firenado, fire swirl ,or fire twister – is a whirlwind induced by a fire and often made up of flame or ash. They usually start with a whirl of wind or smoke. Fire whirls may occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can contract into a tornado-like vortex that sucks in burning debris and combustible gases.

Fire whirls are sometimes colloquially called fire tornadoes, but are not usually classifiable as tornadoes as the vortex in most cases does not extend from the surface to cloud base. Also, even in such cases, even those fire whirls are not classic tornadoes, in that their vorticity derives from surface winds and heat-induced lifting, rather than a tornadic mesocyclone aloft. The literal fire tornado is a rare phenomenon, much more powerful and destructive than the a typical fire whirl, in which the wildfire generates a pyrocumulonimbus cloud that then spawns a tornado. When this tornado forms in or enters the fire zone, it fans flames enormously, draws flame and burning debris into itself, and scatters burning debris over a wide area.

A fire whirl consists of a burning core and a rotating pocket of air. A fire whirl can reach up to 2,000 °F (1,090 °C). Often, fire whirls are created when a wildfire or firestorm creates its own wind, which can turn into a vortex of fire. This causes the tall and skinny appearance of a fire whirl's core.

Most of the largest fire whirls are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present. They are usually 10–50 meters tall, a few meters wide, and last only a few minutes. However, some can be more than a kilometer tall, contain winds over 160 km/h, and persist for more than 20 minutes.

Fire whirls can uproot trees up to 15 metres (49 ft) tall. These can also aid the 'spotting' ability of wildfires to propagate and start new fires as they lift burning materials such as tree bark. These burning embers can be blown away from the fireground by the stronger winds aloft.

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Wikipedia