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Predicting fire thunderstorms

Figure 2: Pyrocumulonimbus from the Sir Ivan fire (12 February 2017). The smoke plume is located between the dashed lines. The Briggs smoke-plume equations describe how the smoke-plume structure changes for various combinations of firepower, fp, and wind speed U, and also how the temperature in the plume decreases with height. Using the temperature and humidity data collected from a weather balloon or forecast model data, the height at the top of the stable barrier, Z, is determined, and the minimum warm humid “boost” θ+, necessary for fire thunderstorms to form, is calculated. This allows the plume temperature at Z to be calculated from θ+, and the corresponding firepower is found by inverting the plume temperature equation. This gives the minimum firepower required for fire thunderstorms to form in this atmospheric environment, a.k.a. the Pyrocumulonimbus Firepower Threshold (PFT). Photo: Sam Crothers NSW RFS.

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