Background
A week before the fires, an exceptional heatwave affected southeastern Australia. From 28–30 January, Melbourne broke records by sweltering through three consecutive days above 43 °C (109 °F), with the temperature peaking at 45.1 °C (113.2 °F) on 30 January, the third hottest day in the city's history.
The heatwave was caused by a slow moving high-pressure system that settled over the Tasman Sea, with a combination of an intense tropical low located off the North West Australian coast and a monsoon trough over northern Australia, which produced ideal conditions for hot tropical air to be directed down over southeastern Australia.[17]
The February fires commenced on a day when several localities across the state, including Melbourne, recorded their highest temperatures since records began in 1859.[18] On 6 February 2009—the day before the fires started—the Premier of Victoria John Brumby issued a warning about the extreme weather conditions expected on 7 February: "It's just as bad a day as you can imagine and on top of that the state is just tinder-dry. People need to exercise real common sense tomorrow".[19] The Premier went on to state that it was expected to be the "worst day [of fires conditions] in the history of the state".
Events of Saturday 7 February
Melbourne air temperature on 7 February 2009 and the preceding and following days.
A total of 3,582 firefighting personnel, mainly from the Country Fire Authority (CFA) and Department of Sustainability and Environment (DSE), were deployed across the state on the morning of 7 February in anticipation of the extreme conditions. By mid-morning, hot northwesterly winds in excess of 100 kilometres per hour (62 mph) hit the state, accompanied by extremely high temperatures and extremely low humidity; a total fire ban was declared for the entire state.
As the day progressed, all-time record temperatures were being reached. Melbourne hit 46.4 °C (115.5 °F), the hottest temperature ever recorded in an Australian capital city,[18] and humidity levels dropped to as low as six percent. The McArthur Forest Fire Danger Index reached unprecedented levels, ranging from 120 to over 200. This was higher than the fire weather conditions experienced on Black Friday in 1939 and Ash Wednesday in 1983.[20]
By midday wind speeds were reaching their peak, and by 12:30 pm powerlines were fallen in Kilmore East by the high winds. These sparked a bushfire that would later generate extensive pyrocumulus clouds, and become the largest, deadliest, and most intense firestorm ever experienced in Australia's post-European history. The overwhelming majority of fire activity occurred between midday and 7:00 pm, when wind speed and temperature were at their highest, and humidity at its lowest.
