Pyrocumulonimbus Firepower Threshold: Assessing the Atmospheric Potential for pyroCb

Abstract Pyrocumulonimbus (pyroCb) clouds are difficult to predict and can produce extreme unexpected wildfire behavior that be very hazardous fire crews. Many forecasters modify conventional thunderstorm diagnostics pyroCb potential, by adding temperature (? ? ) moisture increments q represent smoke plume thermodynamics near the expected condensation level. However, estimating these ? is a highly subjective process requires expert knowledge of all factors might influence future size intensity. In this paper, instead trying anticipate for particular fire, minimum firepower required generate given atmospheric environment considered. This concept, termed threshold (PFT) only information, removing need estimates contribution. A simple approach calculating PFT presented incorporates basic plume-rise physics, yielding an analytic solution offers important insight into formation. Minimum deep, moist convection, plus cloud-base height ( z fc ), diagnosed on thermodynamic diagram. Briggs’s rise equations used convert , mean horizontal wind speed U measure PFT: heat flux entering base plume. proportional product square . Plume insights provided discussed, selection examples presented.