Wind is air pressure on the move. When air pressure changes at a rapid rate it can produce a wind storm. A hot, dry wind storm and fire will produce a firestorm. A firestorm forms when the updraft of a rising column of hot, dry air over an intense original fire mushrooms causing low and very rapidly falling barometric pressure. It takes a hot, dry wind, driven by a very rapidly falling barometric pressure to aid its formation. This fire wind can occur when there is a strong upper level low pressure area north of the original fire or when a low level jet stream is present over or near the fire. The jet stream contributes to creating low pressure areas at the surface. The pressure gradient causes strong to Gale Force winds to converge on the fire bringing in more and more cooler surrounding air to the lower pressure centre - the Chimney Effect.

Firestorm Conditions occur when a fire exists and a pressure fall of 7 mb or more has occurred during the last 3 hours provided:

• ■ low pressure is sustained below 990 mb, and
• ■ the temperature is sustained above 40^oC.

Firestorms have been known to have the energy equivalent up to 40 times that of a typical wildfire. The very rapid fall in barometric pressure prior to the onset of a firestorm can produce impaired concentration and relatively poorer decision making. You cannot fight a firestorm. Immediate evacuation is your best option.

The risk of firestorms has increased as the number of hot days and the length of heatwaves has increased with human-induced climate change. The last three decades has seen an increase in severe storm intensity as measured by their maximum sustainable wind speed. These include cold sea storms and firestorms.

Anatomy of an unstoppable firestorm