Every year presents a challenge to BOM, EMV, etc., on how to warn us of bad or "spike" bushfire potential days without overdoing it.
To help avoid us being turned off by bushfire threat warnings we need to understand the relationship between weather and the quantity and dryness of bushfire fuel.
Currently, next Saturday, 6 January 2018, is shaping up as a day we should be wary of predicts the BOM:
"Very hot and sunny day with fresh north to northwesterly winds, gusty at times. Winds tending fresh and squally southwesterly from the west in the afternoon with a cool change, reaching the central districts during the evening."
Yesterday, bushfire scientist David Packham provided the following advice concerning the bushfire threat anticipated for next Saturday. I have highlighted in red the parts that convey the message. Remember, ember attack is the main cause of fire spread, clearly obvious from the extent that fire reached into the settled areas of California a short time ago.
“In a paper discussing bushfire conditions published in Geophysical Research Letters ( American Geophysical Union, 19 Feb 2015), Prof Michael Reeder (Monash Uni), Thomas Spengler (Uni of Bergen) and Ruth Musgrave ( Scripps Inst. Oceanography, Uni of California) showed a connection between extreme bushfire weather and the breaking of the Rosby waves as indicated by extreme cold fronts.
“There is an average of 1.4 extreme cold fronts per year. Extreme cold fronts are defined as a difference of more than 17 deg C between the max temperature before the cold front and the max temperature on the day after. The most extreme cold front between 1979 and 2010 was 24.3deg C and the most extreme on record (13 Dec 1924(which was 24.9 deg). So much for "earlier than ever" fright speak.
“Reeder, Spengler and Musgrave summarises as "most of the catastrophic fires in the State of Victoria have been associated with the passage of extreme cold fronts".
“Saturday next (6 Jan 2018) is one of those days with a forecast temperature difference of 41- 20 =21 degrees. It is a very extreme cold front indeed.
“My estimate for the Forest Fire Danger Index is 48 for Melbourne Airport which is just in the "Extreme" category (Black Saturday 2009 was about 135). We can expect 1.5 kph rates of spread, non-survival crown fire and spot fire up to 5km ahead of a forest fire in the 25-30 tonne per hectare forest fuels.
“Because our catastrophic fires are associated with an extreme front does NOT mean that every extreme cold front has a major fire attache, fuel and dryness are as important.
There is the highest levels of fuel now available for thousands of years now that prescribed burning has just about ceased. What will save us next Saturday is the early season moisture. The Keetch-Byram Index (KBDI) for Melbourne airport (a good surrogate for all Victoria) is only15mm out of a max. of 200mm and not of concern until greater than 100mm. My "average" for Victoria (except the Mallee) is 36mm and with average drying the concerning level of 100mm will not be reached until the middle of March as the bushfire season finishes. So far the KBDI is showing a "normal" seasonal increase.
“So for next Saturday I can see very hot winds, heaps of fuel and damaging fires but not catastrophic due to residual moisture in the bush.
“There will be fires and some damage but it is too early and moist in this season for a catastrophe.”
I’ve known David Packham for many years and respect his opinion on bushfire (wildfire) and consequently provide the above as a useful item of intelligence to assist our planning for next Saturday.
Again, remember that ember attack is the main cause of fire spread. Many homes have been lost because of the "leave early" policy and many lives lost because people left it too late to leave or did not know to shelter until the fire front had passed.
The photo is from an on-line story by KTLA 5 TV News and is of "several homes destroyed in the Thomas Fire are seen on Dec. 5, 2017" and is worth looking at. To me, the question must be, how many of the homes lost would still be there if the residents had stayed to deal with ember attack?
One person's fight
Having heard the owner, Peter Lang, interviewed on a recent podcast I went hunting.
Owner of Safari West, Peter Lang's inspirational story published on-line in SFGate, San Francisco, but unfortunately you'll need to pick your way through the advertisements.
To me, one of Peter's comments stands out:
“We were able to extinguish that,” he said. “I use the big ‘we.’ Me and that hose. We are the we.”
Finally, remember we are looking at Saturday and the weather can be fickle.
It will be interesting how the agencies handle advice to the public.
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