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.

Missing News: Urban Heat Island effect at Laverton, VICTORIA

ABC finally discovers the Urban Heat Island Effect with this story that reports on a paper that uses climate models to forecast alarming future urban temperatures.

The UHI effect has a significant impact on temperature and is derived from man-made changes in the energy balance in urban centres, to the point where sites that are affected are not useful for monitoring climate unless they are adjusted. The bias arises as a direct result of two different but associated processes. The first involves direct heating of the air surrounding an instrument from vehicle emissions, air-conditioning, industry etc. The second involves land surface changes that include changes over time due to human influence in albedo (change in vegetation for instance), thermal aerodynamic properties (buildings that change air flow around a site), hydrology (affects evaporation) and morphology of the surface.

You'd think that Australia's Bureau of Meteorology would take steps to ensure station weather stations potentially affected by UHI were removed from its climate reference network. It seems that based on a letter featured on Watts up with that, that BOM has ignored investigating potential UHI for at least one of these "High Quality" stations. How many others are out there? Will the ABC investigate?

Note that as of 12:20pm 24 June 2010 AEST the post at WUWT shows a photo of Laverton Western Australia. The weather station in question is Laverton Victoria, not Western Australia. The station is indicated by the place mark in the image below (upper middle). While the local siting may be reasonable, the affect of encroaching development remains un-accounted for.
(Update: WUWT provide a corection and more analysis of Laverton data HERE)

Figure below is a comparison of temperature as recorded at BOM's Laverton station and population growth for the Laverton area. The recent increase in temperature trends appears linked to a rapid increase in population.

Out of interest the Mean Max temp for Laverton Western Australia appears to have dropped since the late 1970s. You can compare temperature data at BOM's climate data site:
http://www.bom.gov.au/climate/data/index.shtml

Laverton WA Station ID 12045 covers 1900-1970-mean max temp over this period is about 27.45 C.
Laverton AERO Station ID 12305 covers 1990-2010 with a mean temp of 26.8 C.  Gross cooling of about 0.65 C - WUWT!