Wind has an extremely powerful effect on fire spread, and when combined with steep slopes can easily increase the rate of spread of a fire by a significant amount. For example, wind gusts of 50 km/h, like was experienced in the Blue Mountains over the weekend, combined with slopes of around 20 degrees, can potentially increase a fire's rate of spread by a factor of about 12 compared to the rate it would spread on flat ground in the absence of wind. Moreover, recent research has indicated that on very steep slopes with strong winds, a fire can exhibit continual acceleration to extreme rates of spread, and the formation of deep flaming zones, which make fire suppression extremely problematic. The direction of the winds in the Blue Mountains over the weekend could have also moved warmer and drier inland air over the region, which would have further exacerbated the fire behaviour.

The midwinter Blue Mountains fire has a few messages:

1. High temperatures are not essential for severe fires - dry fuels and strong winds can create uncontrollable fire. This is particularly significant for Tasmania, we can get extremely strong winds and dry fuels outside the 'normal' bushfire seasons (summer months).

2. Setting clear start and end dates for fire seasons is extremely difficult for Australia given the very high between year and within year climate variability.

3. Because of the high variability it is extremely difficult to attribute odd events like the Blue Mountains fire to climate change. 

4. Our recent global study showed lengthening of fire seasons globally since the late 1970s but this trend was not apparent for Australia because of high variability. See http://www.abc.net.au/science/articles/2015/07/15/4273580.htm

5. But we cannot disprove that climate change is behind the Blue Mountains fire.  

6. If climate change is at work then this is a big worry as more extreme (and seasonally odd) events like this are going to make many bushland communities very hazardous places to reside.