An extensive portion of Australia is under very dry conditions with high fire danger conditions indicated by the highest scale on the Haines Index. The Haines Index is a scale which is derived basically from the lapse rates between two pressure levels and low relative humidity at one of those levels. What this index is aimed to indicate are regions of potent fire behaviour such that plumes are able to rise rapidly in the case of a bushfire. Often in extreme fire conditions with high Haines Index, pyrocumulonimbus clouds are seen atop very large fires and the fire itself virtually creates its own inflow and outflow conditions allowing the fire to be impossible or difficult to control. The recent fires at Halls gap western Victoria and the Black Saturday bushfires 5 years ago indicated this type of behaviour with lightning being observed from the cumulonimbus cloud forming as a result of the raging bushfire.
http://graphical.weather.gov/definitions/defineHaines.html
Catastrophic Fire Danger Definition
http://www.rfs.nsw.gov.au/file_system/attachments/Attachment_FireDangerRating.pdf
Catastrophic fire danger levels were experienced in parts of eastern South Australia on the 8th February.
Now Tasmania is under major alerts for fires today. 
Too easy to cover Tasmania in red with a total fire ban. Anyone in Tasmania know how bad conditions are going to get due to fires already in effect?
Incidentally Victoria was also under extreme fire conditions prior to the change passing through!