We have previously written about events described as “fire tornadoes”, but research led by Rick McRae in Australia has us convinced that those should be more accurately called fire whirls, not tornadoes. We were never very comfortable using the term “fire tornado” for those events, but it has become common and we were not aware, until now, that a phenomenon many times more powerful existed.
Mr. McRae documented what was unquestionably a real fire tornado that occurred near Chapman, ACT, Australia during the McIntyres Hut Fire January 18, 2003.
Researchers had speculated about the ability of a fire to produce a tornado, but this is the first documentation of the creation of a true tornado by the convection column of a large fire.
In a video interview (scroll down and view the second video) and in a paper published October, 2012 in the journal Natural Hazards, he described a fire tornado as occurring over a vegetation fire, a process now known as the phenomenon of “pyro-tornadogenesis”. Under certain conditions, a fire can cause a pyro-cumulus cloud to form, which is not in itself unusual over a large fire. If the cloud continues to build, it can generate lightning, rain, and hail, much like a conventional large thunderstorm. And large thunderstorms can sometimes propagate a tornado, which is what happened over the McIntyrres Hut Fire.
Mr. McRae’s research determined that the fire tornado was moving across the ground at 30 kph (19 mph), had horizontal winds of 250 kph (149 mph), and vertical winds of 150 kph (93 mph).
Dr. Jason Sharples, also associated with the research, described the differences between a fire tornado and a fire whirl:
Tornadoes are associated with thunderstorms and as such they are anchored to a thundercloud above, and are able to sporadically lift off the ground. Fire whirls, on the other hand, are anchored to the ground and do not require the presence of a thunderstorm.
Rick McRae is a Special Risks Analyst at the ACT Emergency Services Agency.
Thanks go out to Chris