The fires currently searing through the Australian bush between Lithgow and Bilpin could create an unusual cloud formation known as a ‘Fire Cloud’ or pyrocumulus, predict fire analysts. The unique weather phenomenon only forms when areas of intense heat, such as bush fires or volcanoes, meet with an unstable atmosphere.
As fires burn, the hot air generated rises in a huge column upwards, with the space underneath being filled by cooler air, a process producing a convection column. The hot-air columns created can be extremely large and can rise high into the atmosphere carrying a large amounts of water vapour – one of the main combustion products of fire.
According to Dr. Sullivan, a senior research scientist, an unstable atmosphere allows these columns to rise higher and higher into the atmosphere, where cooler temperatures condense the water vapour into pyrocumulus clouds. While the clouds do not typically contain enough rain to extinguish the fires, their effect is unpredictable, as they may generate lightning which has been known to start further fires. Strong winds can also fan fires, and in extreme cases, very high wind speeds can cause ‘fire tornadoes’.
A representative from the Rural Fire service, Natalie Sanders, reported that a pyrocumulus had already appeared over the State Mine fire last Thursday, and the same conducive weather conditions were forecast over the Lithgow region for Wednesday, when, Rural Fire Service Commissioner Shane Fitzsimmons warned, after several cooler days, temperatures of over 30C (86F) are predicted to peak.
A State of Emergency has been predicted in the New South Wales area, and mandatory evacuations are being planned.
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