Understanding fire weather (Bureau of Meteorology, 2017)
"When the weather is hot, humidity (moisture in the atmosphere) is low and there’s been little recent rain, vegetation dries out and becomes more flammable. Periods of wet weather can encourage vegetation growth, increasing the amount of fuel available—and future bushfire risk, if dry weather follows.
Strong, gusty winds help fan flames and will cause a fire to spread faster across the landscape, reducing the time you have to prepare.
Above the fire, strong winds can carry hot embers long distances. These can start ‘spot’ fires many kilometres ahead of the main fire front.
A change in wind direction can bring a dangerous period of bushfire activity. This is often seen as a trough or cold front (also known as a cool change) shifting the direction of the wind, altering the course of the fire and broadening the fire front.
Lightning, produced by thunderstorms, can ignite bushfires. Large fires can also create their own thunderstorms. These are known as pyrocumulonimbus, and are caused by the heat of the fire forcing the smoke and hot air above it to rise to the point where it cools and condenses into water droplets, eventually forming large clouds."