The so called fire tornado or fire whirls generally form when superheated air near the surface of a large fire zone rises rapidly in an airmass where sufficient horizontal or vertical vorticity (spin in the atmosphere) is also present. Much like a dust devil or whirlwind, the rapidly rising air above a wildfire can accelerate and turn the local vorticity into a tight vertical vortex, now composed of fire instead of dust.
Oct
2
2012