Wednesday, March 7, 2012

BOM, Exactly wrong?

Always enjoy looking back at what the Magic 8 ball predicted.

Here's the BOM's Karl Braganza on The World Today in September 2011

SIMON LAUDER: The last La Nina was strong enough to push the rainfall south, drenching New South Wales and Victoria. Dr Braganza says it’s unlikely this summer's rainfall will be as heavy and there will be clearer signs about what's in store soon. 

KARL BRAGANZA: Another month we'll know for sure whether we are going to see a La Nina over the summer months and that still gives you a little bit of time ahead of cyclone season and other season and the monsoon season or the wet season up north, to really understand whether we are going to impact on that. 

Yeah, in terms of the magnitude of that La Nina, it will be unlikely at this point that it is going to be as strong as it was over 2010/11. So what that generally means for Australia is you get an enhanced wet season in the tropics but not necessarily a whole lot of rainfall over the rest of the continent

Karl Braganza again on PM on January 4.
Dr Braganza says while La Nina's influence continues it is loosening its grip, and big floods aren't expected on the same scale this year.
"It's a weaker event this time round, compared to last summer, so we had those terrific floods at the end of 2010 and into 2011," he said.
"We might still get very heavy monsoonal rainfall. That can happen in any year in Australia, but probably the odds aren't on for the type of flooding we saw in the summer just gone."
So what happened?
Here's BOM's summary of January 2012 rainfall
January rainfall was generally above average for most of the country, but below average for parts of northern central Australia and the tropical north.

Here's February 2012
February rainfall was generally above average for the south-eastern mainland, and below average for parts of northern Australia, particularly northern Western Australia and the Top End.
In the last days of February, a slow moving low pressure trough extending from central Australia through Victoria and very moist tropical airflow brought record breaking rainfall for central and northern Victoria, extending into southern New South Wales, causing flash flooding in some areas. The trough then brought particularly heavy falls in a wide band stretching from central Australia, through northern South Australia and western New South Wales to the Illawarra, causing further flooding and road closures.

Here's a photo of the Warragamba Dam spilling over on March 2, 2012 from those summer rains.
From SCA

Updated from yesterday.


  1. Braganza,two months back,looks at the numbers and states that another heavy southern flood event is probably not odds-on.

    Is that a problem? He was talking about likelihoods,not ruling out the possibility altogether. He noted that SOI was not strongly positive and La Nina weakening.

    Of all periods of La Nina [SOI 8+] in the record,how many have produced consecutive year extreme/record setting rain and flood events in the Murray and Murrumbidgee catchments? Do you know the answer?

    How do you spin 'BOM,exactly wrong?' out of the excerpts you quote?

  2. "Is that a problem?"
    Certainly is if you claim to be an expert.

    "How do you spin 'BOM,exactly wrong?' out of the excerpts you quote?"
    The observations are almost completely opposite to the prediction. In any other world this would be a pretty good example of a complete stuff up, except perhaps for yours.

    1. "Stuff up?" This was not in any way a forecast or prediction! The REAL forecasts from modelling and observation were very accurate for timing,location and quantity given real world resolution of the models.

      Braganza did not even attempt a forecast two months out,yet you somehow think he has. He was talking about the climatology. This is what you can expect based on precedent,not what you get now and then.

      Clearly,every time a climatologist makes some comments about climate and likelihood a disclaimer will have to be read out to remind slower listeners they are not listening to a new BOM forecasting service of similar claimed performance to daily and weekly ones.

      In 'my world',the real world,and in the Riverina,BOM's week to week forecasting has been fine. In my world,the real one,their probabalistic forecasts have been good too...but that's because I understand the limits of their scope.I also understand that when a probabalistic forecast is unsuccessful,it tells you that what eventuated was unusual relative to the period of observed past that informs the probabilities.

      In 'my world',the real world,Braganza was absolutely spot on in saying that another major flood event of the scale of last summers was unlikely...IOW, talking about the odds for an extreme event. What we just saw was a_very_rare_event. In fact it set many three,five and seven day records for rainfall for periods from 40 to 120 years. Do you appreciate that? No-one can actually quantitatively and spatially forecast rain in inland Australia from eight weeks away,let alone a record event. But they can talk about likelihood,or is that now forbidden in case someone mistakes it for a forecast?

      "On March 5th,Farmer X complained that he lost his stock,pumps and equipment because he heard Karl Braganza on Jan 4th say that a major flood event like 2011's was unlikely" That's pretty much what you're trying on here.

  3. I'll have another look at the output of Bom's magic 8 ball when this year's cyclone season is over. Be sure to come back and have a look then.
    In the "real world" as opposed to the world portrayed in the guts of a computer climate model, the cyclone outlook isn't looking like coming close to the forecast(seems similar to the poor forecasting skill revealed in the comparison above). If that comes to pass I'll once again have cause to pose the question: BOM exactly wrong?

  4. Be mindful...“It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong”. Richard Feynman


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