Bureau of Meteorology database bug

With temperatures in Western Australia and across the country in 2009/2010 reported by the Bureau of Meteorology to be among the hottest ever recorded, it's worth being aware of database adjustments made by the BOM during that period.

BOM data indicates that Australia’s annual mean temperature for 2009 was .9°C above the 1961/90 average, making it the country’s second warmest year since "high quality" records began in 1910. WA's average temperature during the 12 months to the end of June 2010 was 23.55°C, matching the previous record.

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I maintain a 100 year temperature comparison on my site at waclimate.net based on 32 locations in WA with fairly consistent BOM records dating to the late 1800s / early 1900s.

The 32 locations in WA are Albany, Balladonia, Bridgetown, Broome, Bunbury, Busselton, Cape Leeuwin, Cape Naturaliste, Carnarvon, Derby, Donnybrook, Esperance, Eucla, Eyre, Geraldton, Halls Creek, Kalgoorlie, Katanning, Kellerberrin, Laverton, Marble Bar, Merredin, Mt Barker, Northam, Onslow, Perth, Rottnest Island, Southern Cross, Wandering, Wiluna, Wyndham and York.

In summary, my calculation of the BOM data records shows that, based on these 32 locations, the average annual minimum around the year 1900 was 12.96C and the average annual maximum was 25.12C.

Other analyses of the BOM's historic data for these 32 locations might calculate the averages a few points of a degree higher or lower, dependent upon different criteria, but it is irrelevant in the context of this discussion as 12.96C and 25.12C are the fixed baselines for all my minimum and maximum comparisons since 2008.

I update my website each month with the latest BOM data and when doing my update in December 2009 I noticed the mean minimum and maximum temperatures had all been adjusted up by about half a degree from the temperatures that had previously been recorded on the BOM website database for August 2009.

Below are the 32 locations with their original data in the top green row as posted by the BOM from September 1 to November 17, and their new adjusted data in the red row below:

August 2009:

	Min	Max		Min	Max		Min	Max		Min	Max
Albany	9	16.2	Balladonia	5	20.7	Bridgetown	5.7	15.7	Broome	14.6	29.2
	9.4	16.6		5.5	21.1		6.2	16.1		15.1	29.7

Bunbury	8.2	16.7	Busselton	8.7	17	Cape Leeuwin	11.8	16.2	Cape Naturaliste	10.5	16.7
	8.7	17.2		9.2	17.4		12.2	16.6		11	17.1

Carnarvon	11.4	23.2	Derby	15	32.7	Donnybrook	6.7	17.2	Esperance	8.3	17.7
	11.8	23.6		15.6	33.2		7.2	17.6		8.8	18.1

Eucla	7.9	21.5	Eyre	4.3	21.6	Geraldton	9.5	20	Halls Creek	16.1	32.6
	8.4	21.9		4.5	22		10	20.5		16.6	33

Kalgoorlie	6.8	20.3	Katanning	6.1	14.7	Kellerberrin	5.3	18.6	Laverton	7.5	22.4
	7.2	20.7		6.5	15.1		5.6	18.9		7.9	22.9

Marble Bar	13.8	31.1	Merredin	6.1	17.7	Mt Barker	6.8	15.6	Northam	6.2	18.4
	14.3	31.5		6.5	18.1		7	15.8		6.6	18.7

Onslow	13.8	27.7	Perth	8.8	18.5	Rottnest Island	12.4	17.3	Southern Cross	4.6	18.1
	14.3	28.1		9.3	18.9		12.9	17.7		5	18.6

Wandering	5.3	16.1	Wiluna	7.5	24.8	Wyndham	18.3	34	York	5.6	17.9
	5.6	16.6		7.7	25.2		18.8	34.4		5.9	18.3

		As recorded from September 1 to November 17 2009 on BOM web database

		As recorded since November 17 2009 following correction to BOM database bug

I questioned the BOM as to what had happened and on December 7 2009 received this reply …

"Thanks for pointing this problem out to us. Yes, there was a bug in the Daily Weather Observations (DWO) on the web, when the updated version replaced the old one around mid November. The program rounded temperatures to the nearest degree, resulting in mean maximum/minimum temperature being higher. The bug has been fixed since and the means for August 2009 on the web are corrected."

The temperatures for all WA locations in the BOM web database remain at the higher adjusted temperatures for August 2009 and there was no change from the adjustment made on November 17 prior to my correspondence.

I was confused by this so I sent another question to the BOM, as below and with the response on December 9 ...

"Thanks for the reply but I'm still a bit puzzled. Below are August 2009 min and max data for 32 WA sites I keep an eye on, the top temps being those recorded on the BoM website from Sep 1 to Nov 17, and the bottom temps the updated version since Nov 17. The rounded temperature bug seems to have only affected August as there has been no adjustment to any other month including September. I've just checked the BoM site and there's no change to the August data. Can you please let me know which of the temps below are correct?"

Reply: "The bottom ones are correct. The bug only affected averages for August 2009."

Since then I have continued to update my site each month with BOM data to compare the ongoing 12 month average at 32 WA locations with my fixed 1900 baseline of minimum 12.96C and maximum 25.12C ...

Year to March 2009	Year to April 2009	Year to May 2009	Year to June 2009
min .29C above the early 1900s	min .33C above the early 1900s	min .25C above the early 1900s	min .29C above the early 1900s
max .68C above the early 1900s	max .79C above the early 1900s	max .75C above the early 1900s	max .69C above the early 1900s

Year to July 2009	Year to August 2009	Year to September 2009	Year to October 2009
min .31C above the early 1900s	min .51C above the early 1900s	min .44C above the early 1900s	min .39C above the early 1900s
max .64C above the early 1900s	max .72C above the early 1900s	max .60C above the early 1900s	max .60C above the early 1900s

Year to November 2009	Year to December 2009	Year to January 2010	Year to February 2010
min .53C above the early 1900s	min .59C above the early 1900s	min .54C above the early 1900s	min .60C above the early 1900s
max .92C above the early 1900s	max 1.09C above the early 1900s	max 1.16C above the early 1900s	max 1.28C above the early 1900s

Year to March 2010	Year to April 2010	Year to May 2010	Year to June 2010
min .75C above the early 1900s	min .80C above the early 1900s	min .85C above the early 1900s	min .80C above the early 1900s
max 1.37C above the early 1900s	max 1.35C above the early 1900s	max 1.29C above the early 1900s	max 1.31C above the early 1900s

Year to July 2010	Year to August 2010	Year to September 2010	Year to October 2010
min .74C above the early 1900s	min .63C above the early 1900s	min .63C above the early 1900s	min .56C above the early 1900s
max 1.32C above the early 1900s	max 1.27C above the early 1900s	max 1.34C above the early 1900s	max 1.34C above the early 1900s

Year to November 2010	Year to December 2010	Year to January 2011	Year to February 2011
min .56C above the early 1900s	min .61C above the early 1900s	min .68C above the early 1900s	min .72C above the early 1900s
max 1.37C above the early 1900s	max 1.23C above the early 1900s	max 1.17C above the early 1900s	max 1.02C above the early 1900s

Year to March 2011	Year to April 2011	Year to May 2011	Year to June 2011
min .69C above the early 1900s	min .67C above the early 1900s	min .69C above the early 1900s	min .75C above the early 1900s
max .95C above the early 1900s	max .95C above the early 1900s	max .93C above the early 1900s	max .94C above the early 1900s

Year to July 2011	Year to August 2011	Year to September 2011	Year to October 2011
min .88C above the early 1900s	min .97C above the early 1900s	min .96C above the early 1900s	min 1.07C above the early 1900s
max .96C above the early 1900s	max 1.05C above the early 1900s	max 1.06C above the early 1900s	max .99C above the early 1900s

Year to November 2011	Year to December 2011	Year to January 2012	Year to February 2012
min 1.04C above the early 1900s	min 1.10C above the early 1900s	min 1.09C above the early 1900s	min 0.99C above the early 1900s
max .84C above the early 1900s	max .88C above the early 1900s	max .81C above the early 1900s	max .85C above the early 1900s

Year to March 2012	Year to April 2012	Year to May 2012	Year to June 2012
min .99C above the early 1900s	min .86C above the early 1900s	min .79C above the early 1900s	min .78C above the early 1900s
max .86C above the early 1900s	max .89C above the early 1900s	max .95C above the early 1900s	max .95C above the early 1900s

Year to July 2012	Year to August 2012	Year to September 2012	Year to October 2012
min .57C above the early 1900s	min .48C above the early 1900s	min .54C above the early 1900s	.54C above the early 1900s
max .96C above the early 1900s	max .97C above the early 1900s	max 1.06C above the early 1900s	1.22C above the early 1900s

Year to November 2012	Year to December 2012	Year to January 2013	Year to February 2013
min .52C above the early 1900s	min .53C above the early 1900s	min .54C above the early 1900s	min .56C above the early 1900s
max 1.25C above the early 1900s	max 1.35C above the early 1900s	max 1.44C above the early 1900s	max 1.56C above the early 1900s

Year to March 2013	Year to April 2013	Year to May 2013	Year to June 2013
min .61C above the early 1900s	min .79C above the early 1900s	min .92C above the early 1900s	min .89C above the early 1900s
max 1.46C above the early 1900s	max 1.56C above the early 1900s	max 1.49C above the early 1900s	max 1.49C above the early 1900s

Year to July 2013	Year to August 2013	Year to September 2013	Year to October 2013
min 1.01C above the early 1900s	min 1.14C above the early 1900s	min 1.24C above the early 1900s	min 1.21C above the early 1900s
max 1.51C above the early 1900s	max 1.53C above the early 1900s	max 1.46C above the early 1900s	max 1.42C above the early 1900s

Year to November 2013	Year to December 2013	Year to January 2014	Year to February 2014
min 1.31C above the early 1900s	min 1.23C above the early 1900s	min 1.17C above the early 1900s	min 1.12C above the early 1900s
max 1.51C above the early 1900s	max 1.47C above the early 1900s	max 1.43C above the early 1900s	max 1.29C above the early 1900s

Year to March 2014	Year to April 2014	Year to May 2014	Year to June 2014
min 1.17C above the early 1900s	min 1.01C above the early 1900s	min 1.08C above the early 1900s	min 1.03C above the early 1900s
max 1.31C above the early 1900s	max 1.19C above the early 1900s	max 1.22C above the early 1900s	max 1.24C above the early 1900s

Year to July 2014	Year to August 2014	Year to September 2014	Year to October 2014
min 1.07C above the early 1900s	min 1.03C above the early 1900s	min 1.03C above the early 1900s	min 1.10C above the early 1900s
max 1.22C above the early 1900s	max 1.29C above the early 1900s	max 1.41C above the early 1900s	max 1.46C above the early 1900s

Year to November 2014	Year to December 2014	Year to January 2015	Year to February 2015
min 1.02C above the early 1900s	min 0.99C above the early 1900s	min 0.98C above the early 1900s	min 1.09C above the early 1900s
max 1.41C above the early 1900s	max 1.35C above the early 1900s	max 1.37C above the early 1900s	max 1.56C above the early 1900s

Year to March 2015	Year to April 2015	Year to May 2015	Year to June 2015
min 1.07C above the early 1900s	min 1.05C above the early 1900s	min 0.83C above the early 1900s	min 0.95C above the early 1900s
max 1.46C above the early 1900s	max 1.45C above the early 1900s	max 1.37C above the early 1900s	max 1.47C above the early 1900s

Year to July 2015	Year to August 2015	Year to September 2015	Year to October 2015
min 0.98C above the early 1900s	min 0.97C above the early 1900s	min 0.83C above the early 1900s	min 0.88C above the early 1900s
max 1.49C above the early 1900s	max 1.34C above the early 1900s	max 1.31C above the early 1900s	max 1.43C above the early 1900s

Year to November 2015	Year to December 2015	Year to January 2016	Year to February 2016
min 0.98C above the early 1900s	min 0.99C above the early 1900s	min 1.07C above the early 1900s	min 0.93C above the early 1900s
max 1.54C above the early 1900s	max 1.57C above the early 1900s	max 1.50C above the early 1900s	max 1.38C above the early 1900s

Year to March 2016	Year to April 2016	Year to May 2016	Year to June 2016
min 1.02C above the early 1900s	min 1.13C above the early 1900s	min 1.21C above the early 1900s	min 1.16C above the early 1900s
max 1.41C above the early 1900s	max 1.50C above the early 1900s	max 1.55C above the early 1900s	max 1.38C above the early 1900s

Year to July 2016	Year to August 2016	Year to September 2016	Year to October 2016
min 1.11C above the early 1900s	min 1.03C above the early 1900s	min 0.95C above the early 1900s	min 0.72C above the early 1900s
max 1.30C above the early 1900s	max 1.20C above the early 1900s	max 0.97C above the early 1900s	max 0.68C above the early 1900s

Year to November 2016	Year to December 2016	Year to January 2017	Year to February 2017
min 0.58C above the early 1900s	min 0.56C above the early 1900s	min 0.40C above the early 1900s	min 0.36C above the early 1900s
max 0.64C above the early 1900s	max 0.58C above the early 1900s	max 0.57C above the early 1900s	max 0.39C above the early 1900s

Year to March 2017	Year to April 2017	Year to May 2017	Year to June 2017
min 0.25C above the early 1900s	min 0.10C above the early 1900s	min 0.06C above the early 1900s	min 0.02C below the early 1900s
max 0.34C above the early 1900s	max 0.36C above the early 1900s	max 0.44C above the early 1900s	max 0.63C above the early 1900s

Year to July 2017	Year to August 2017	Year to September 2017	Year to October 2017
min 0.01C below the early 1900s	min 0.08C above the early 1900s	min 0.19C above the early 1900s	min 0.28C above the early 1900s
max 0.73C above the early 1900s	max 0.83C above the early 1900s	max 0.99C above the early 1900s	max 1.06C above the early 1900s

Year to November 2017	Year to December 2017	Year to January 2018	Year to February 2018
min 0.40C above the early 1900s	min 0.43C above the early 1900s	min 0.47C above the early 1900s	min 0.52C above the early 1900s
max 1.04C above the early 1900s	max 1.06C above the early 1900s	max 1.01C above the early 1900s	max 1.03C above the early 1900s

Year to March 2018	Year to April 2018	Year to May 2018	Year to June 2018
min 0.59C above the early 1900s	min 0.67C above the early 1900s	min 0.65C above the early 1900s	min 0.69C above the early 1900s
max 1.16C above the early 1900s	max 1.25C above the early 1900s	max 1.30C above the early 1900s	max 1.18C above the early 1900s

Year to July 2018	Year to August 2018	Year to September 2018	Year to October 2018
min 0.73C above the early 1900s	min 0.62C above the early 1900s	min 0.55C above the early 1900s	min 0.63C above the early 1900s
max 1.23C above the early 1900s	max 1.14C above the early 1900s	max 1.13C above the early 1900s	max 1.11C above the early 1900s

Year to November 2018	Year to December 2018	Year to January 2019	Year to February 2019
min 0.50C above the early 1900s	min 0.51C above the early 1900s	min 0.49C above the early 1900s	min 0.49C above the early 1900s
max 0.96C above the early 1900s	max 1.01C above the early 1900s	max 1.12C above the early 1900s	max 1.32C above the early 1900s

Year to March 2019	Year to April 2019	Year to May 2019	Year to June 2019
min 0.51C above the early 1900s	min 0.46C above the early 1900s	min 0.38C above the early 1900s	min 0.37C above the early 1900s
max 1.31C above the early 1900s	max 1.23C above the early 1900s	max 1.16C above the early 1900s	max 1.17C above the early 1900s

Year to July 2019	Year to August 2019	Year to September 2019	Year to October 2019
min 0.32C above the early 1900s	min 0.36C above the early 1900s	min 0.44C above the early 1900s	min 0.41C above the early 1900s
max 1.16C above the early 1900s	max 1.29C above the early 1900s	max 1.42C above the early 1900s	max 1.55C above the early 1900s

Year to November 2019	Year to December 2019	Year to January 2020	Year to February 2020
min 0.45C above the early 1900s	min 0.57C above the early 1900s	min 0.53C above the early 1900s	min 0.60C above the early 1900s
max 1.76C above the early 1900s	max 2.01C above the early 1900s	max 1.93C above the early 1900s	max 1.85C above the early 1900s

The data shows averaged annual temperature across WA rose sharply from November 2009, the month the BOM software bug was corrected to adjust August 2009 average temperatures up by about half a degree. The above data is graphed below:

BOM monthly data is available for all WA recording locations with historic averages which can be used to verify the trend I calculate from 32 locations compared to 1900 baseline temperatures.

The sharp upward trend compared with the 1900 average is reflected in BOM data below (BOM website source) which shows the overall WA mean temperature jumped by almost 1 degree C beginning in the spring of 2009 between August and November, broken into seasons to give some averaged time perspective.

	Spring 2008 - 23.4C average	Summer 2008/09 - 28.6C average
	Sep 2008 - 20.99C - 1.3C above average	Dec 2008 - 27.4C - .5C below average
July 2008 - 14.39C - 0.42C above average	Oct 2008 - 24.57C - 1.43C above average	Jan 2009 - 29.7C - 1C above average
Aug 2008 - 16.52C - 0.64C below average	Nov 2008 - 24.6C - 1.3C below average	Feb 2009 - 28.7C - .6C above average


Autumn 2009 - 23.1C average	Winter 2009 - 16.9C average	Spring 2009 - 23.6C average
Mar 2009 - 26.7C - 0.1C above average	Jun 2009 - 16.2C - 0.3C above average	Sep 2009 - 20.0C - 0.3C above average
Apr 2009 - 23.8C - 0.6C above average	Jul 2009 - 15.6C - 0.6C above average	Oct 2009 - ?? but above average
May 2009 - 18.7C - 0.2C below average	Aug 2009 - 18.9C - 1.7C above average	Nov 2009 - 27.2C - 1.3C above average


Summer 2009/10 - 29.6C average	Autumn 2010 - 24C average	Winter 2010 - 16.2C average
Dec 2009 - 29C - 1C above average	Mar 2010 - 27.6C - 1C above average	Jun 2010 - 16.6C - 0.7C above average
Jan 2010 - 29.9C - 1.2C above average	Apr 2010 - 25.0C - 1.8C above average	Jul 2010 - 15.3C - 0.3C above average
Feb 2010 - 29.8C - 1.7C above average	May 2010 - 19.4C - 0.5C above average	Aug 2010 - 16.6C - 0.1C above average


Spring 2010 - 22.9C average	Summer 2010/11 - 28.5C average	Autumn 2011 - 22.1C average
Sep 2010 - 19C - 0.7C below average	Dec 2010 - 27.9C - long-term average	Mar 2011 - 25.3C - 1.3C below average
Oct 2010 - 23.1C - long-term average	Jan 2011 - 29.7C - 1C above average	Apr 2011 - 23.1C - 0.1C below average
Nov 2010 - 26.6C - 0.7C above average	Feb 2011 - 27.9C - 0.9C below average	May 2011 - 18.0C - 0.9C below average


Winter 2011 - 16.3C average	Spring 2011 - 22.8C average	Summer 2011/12 - 27.9C average
Jun 2011 - 15.5C - 0.4C below average	Sep 2011 - 19.6C - 0.1C above average	Dec 2011 - 27.9C - 0.1C below average
Jul 2011 - 15.9C - 1C above average	Oct 2011 - 23.4C - 0.2C above average	Jan 2012 - 27.8C - 0.9C below average
Aug 2011 - 17.6C - 1.1C above average	Nov 2011 - 25.3C - 0.6C below average	Feb 2012 - 27.9C - 0.2C below average


Autumn 2012 - 22.5C average	Winter 2012 - 15.9C average	Spring 2012 - 24.2C average
Mar 2012 - 25.4C - 1.2C below average	Jun 2012 - 15.8C - 0.1C below average	Sep 2012 - 21.2C - 1.5C above average
Apr 2012 - 23.2C - long-term average	Jul 2012 - 14.3C - 0.7C below average	Oct 2012 - 24.8C - 1.7C above average
May 2012 - 18.8C - 0.1C below average	Aug 2012 - 17.7C - 1.1C above average	Nov 2012 - 26.7C - 0.8C above average

Note: the ACORN-SAT dataset is being used by the BoM for temperature area averages from December 2012 onwards. For this reason, all averages tabulated above are from a different set of weather stations and in many cases their mean temperatures bear no relationship to the mean temperatures listed below.

Summer 2012/13 - 29.1C average	Autumn 2013 - 23.8C average	Winter 2013 - 16.4C average
Dec 2012 - 28.5C - 0.60C above average	Mar 2013 - 26.6C - 0.02C above average	Jun 2013 - 15.5C - 0.43C below average
Jan 2013 - 30.1C - 1.20C above average	Apr 2013 - 25.2C - 1.96C above average	Jul 2013 - 15.6C - 0.61C above average
Feb 2013 - 28.7C - 0.62C above average	May 2013 - 19.8C - 0.86C above average	Aug 2013 - 18.1C - 1.56C above average


Spring 2013 - 24.3C average	Summer 2013/14 - 28.2C average	Autumn 2014 - 23.9C average
Sep 2013 - 21.1C - 1.37C above average	Dec 2013 - 28.2C - 0.32C above average	Mar 2014 - 27.6C - 1.03C above average
Oct 2013 - 24.9C - 1.77C above average	Jan 2014 - 28.9C - 0.16C above average	Apr 2014 - 23.7C - 0.50C above average
Nov 2013 - 26.8C - 0.90C above average	Feb 2014 - 27.6C - 0.47C below average	May 2014 - 20.3C - 1.38C above average


Winter 2014 - 16.2C average	Spring 2014 - 24.7C average	Summer 2014/15 - 29.4C average
Jun 2014 - 15.9C - 0.05C below average	Sep 2014 - 21.7C - 1.97C above average	Dec 2014 - 28.6C - 0.69C above average
Jul 2014 - 15.2C - 0.21C above average	Oct 2014 - 25.5C - 2.45C above average	Jan 2015 - 29.3C - 0.63C above average
Aug 2014 - 17.7C - 1.18C above average	Nov 2014 - 26.9C - 1.05C above average	Feb 2015 - 30.4C - 2.30C above average


Autumn 2015 - 22.3C average	Winter 2015 - 17.0C average	Spring 2015 - 24.8C average
Mar 2015 - 26.7C - 0.06C above average	Jun 2015 - 17.5C - 1.59C above average	Sep 2015 - 20.4C - 0.72C above average
Apr 2015 - 22.2C - 1.04C below average	Jul 2015 - 15.9C - 0.91C above average	Oct 2015 - 26.4C - 3.28C above average
May 2015 - 18.2C - 0.68C below average	Aug 2015 - 17.6C - 1.10C above average	Nov 2015 - 27.7C - 1.78C above average


Summer 2015/16 - 28.7C average	Autumn 2016 - 24.2C average	Winter 2016 - 16.9C average
Dec 2015 - 28.7C - 0.82C above average	Mar 2016 - 27.9C - 1.34C above average	Jun 2016 - 16.8C - 0.88C above average
Jan 2016 - 28.9C - 0.17C above average	Apr 2016 - 24.8C - 1.60C above average	July 2016 - 17.2C - 0.72C above average
Feb 2016 - 28.6C - 0.46C above average	May 2016 - 20.0C - 1.11C above average	August 2016 - 16.8C - 0.28C above average


Spring 2016 - 23.1C average	Summer 2016/17 - 27.8C average	Autumn 2017 - 23.2C average
Sept 2016 - 19.1C - 0.60C below average	Dec 2016 - 27.9C - 0.0C average	Mar 2017 - 27.2C - 0.57C above average
Oct 2016 - 23.4C - 0.33C above average	Jan 2017 - 28.3 - 0.36C below average	Apr 2017 - 23.1 - 0.09C below average
Nov 2016 - 26.9C - 1.02C above average	Feb 2017 - 27.3C - 0.84C below average	May 2017 - 19.4 - 0.48C above average


Winter 2017 - 16.9C average	Spring 2017 - 24.0C average	Summer 2017/18 - 26.4C average
Jun 2017 - 16.6C - 0.72C above average	Sep 2017 - 20.7C - 0.98C above average	Dec 2017 - 28.5C - 0.63C above average
Jul 2017 - 16.3C - 1.35C above average	Oct 2017 - 24.4C - 1.33C above average	Jan 2018 - 23.4C - 0.16C above average
Aug 2017 - 17.9C - 1.36C above average	Nov 2017 - 26.9C - 1.05C above average	Feb 2018 - 27.4C - 0.66C below average


Autumn 2018 - 24.2C average	Winter 2018 - 16.3C average	Spring 2018 - 23.8C average
Mar 2018 - 27.8C - 1.24C above average	Jun 2018 - 16.4C - 0.46C above average	Sep 2018 - 20.5C - 0.78C above average
Apr 2018 - 25.3C - 2.09C above average	Jul 2018 - 16.4C - 1.39C above average	Oct 2018 - 24.5C - 1.35C above average
May 2018 - 19.4C - 0.47C above average	Aug 2018 - 16.0C - 0.46C below average	Nov 2018 - 26.4C - 0.52C above average


Summer 2019 - 29.9C average	Autumn 2019 - 24.0C average	Winter 2019 - 16.7C average
Dec 2018 - 29.4C - 1.53C above average	Mar 2019 - 28.1C - 2.28C above average	Jun 2019 - 16.2C - 0.30C above average
Jan 2019 - 30.3C - 1.59C above average	Apr 2019 - 24.6C - 1.30C above average	Jul 2019 - 16.6C - 1.59C above average
Feb 2019 - 30.1C - 2.05C above average	May 2019 - 19.4C - 0.46C above average	Aug 2019 - 17.4C - 0.88C above average


Spring 2019
Sept 2019 - 21.3C - 1.64C above average

The statewide data above shows temperatures in the winter of 2018 were 0.8C above the long-term average.

The BOM explains its baseline for the above anomalies thus: The climatological averages shown in the text and tables are generally long-term means based on observations from all available years of record, which vary widely from site to site. They are not shown for sites with less than 30 years of record, as they cannot then be calculated reliably. Climatological extremes are generally taken from available observations from all available years of record. The number of years can vary substantially from site to site.

The BOM also compares temperatures with the baseline average of 22.5C from 1961 to 1990. The BoM's portrayal of WA's temperature history is not static. The animation below shows the difference between the anomaly charts published in 2010 and 2013, the ACORN dataset of 2012 a probable reason for the early years cooling and temperatures warming since about 1930:

The bureau replaced the ACORN 1 temperature dataset of 2012 with a revised ACORN 2 dataset in late 2018, increasing Australia's per decade rate of warming by 23% (see analysis). In Western Australia, this cooled the 1961-90 anomaly baseline mean temperature at all 25 WA network stations from 20.44C in ACORN 1 to 20.15C in ACORN 2. The effect of this 0.29C difference (and further homogenised cooling of temperatures before 1961) can be seen in the animation below:

It is worth noting the frequency of adjustments on the BOM database as presented on the web.

In July 2010 I checked every month back to June 2009 in all 32 locations within my records against the BOM database as currently presented on the web. I found 43 adjustments by the BOM, the most consistent being January 2010 wherein most but not all locations saw a small reduction in their mean maximum:

	Min	Max		Min	Max		Min	Max		Min	Max
Albany	16.4	23.1	Balladonia	16.1	34.4	Balladonia	4.3	21.7	Bridgetown	12.1	30.5
Jan 2010	16.4	23	Jan 2010	16.1	34.1	Sep 2009	4.4	21.7	Jan 2010	12.1	30.4

	Min	Max		Min	Max		Min	Max		Min	Max
Broome	26.6	33.1	Bunbury	15.5	31.7	Busselton	14.7	30.6	Busselton	11.4	23.3
Jan 2010	26.6	33	Jan 2010	15.5	31.6	Jan 2010	14.7	30.5	Apr 2009	11.3	23.3

	Min	Max		Min	Max		Min	Max		Min	Max
Cape Leeuwin	17.3	23.2	Cape Naturaliste	15.2	27.7	Carnarvon	22.5	30.8	Derby	25	39.4
Jan 2010	17.3	23.1	Jan 2010	15.2	27.6	Jan 2010	22.5	30.9	Nov 2009	25	39.5

	Min	Max		Min	Max		Min	Max		Min	Max
Derby	26.5	36.5	Donnybrook	15.9	33.1	Esperance	16.1	27.8	Esperance Airport	15	29.4
Feb 2010	26.4	36.5	Jan 2010	15.9	33	Jan 2010	16.1	27.6	Jan 2010	15	29.2

	Min	Max		Min	Max		Min	Max		Min	Max
Eucla	18.2	30.3	Eyre	14.3	30.9	Geraldton	18.3	33	Halls Creek
Jan 2010	18.2	30.1	Jan 2010	14.3	30.7	Jan 2010	18.3	32.9		*	*

	Min	Max		Min	Max		Min	Max		Min	Max
Kalgoorlie	19.8	36.8	Katanning	13.1	31.2	Kellerberrin	8.3	26.8	Kellerberrin	14.7	34.4
Jan 2010	19.8	36.6	Jan 2010	13.1	31.1	Oct 2009	8.9	27.2	Dec 2009	14.5	34.4

	Min	Max		Min	Max		Min	Max		Min	Max
Kellerberrin	16.5	38	Kellerberrin	17.5	35.8	Kellerberrin	10.6	27.9	Laverton
Jan 2010	16.3	37.8	Feb 2010	17.6	36	Apr 2009	10.6	27.8		*	*

	Min	Max		Min	Max		Min	Max		Min	Max
Marble Bar	26.8	41.9	Merredin	18.5	37.6	Mt Barker	7	14.8	Mt Barker	11.8	27.9
Jan 2010	26.8	42	Feb 2010	18.5	37.4	Sep 2009	6.3	14.9	Jan 2010	11.8	28.3

	Min	Max		Min	Max		Min	Max		Min	Max
Northam	17.7	37.4	Onslow	24	36.3	Perth Metro	18.9	33.5	Rottnest Island	16	23.6
Jan 2010	17.7	37.3	Jan 2010	24	36.6	Jan 2010	18.9	33.4	Nov 2009	16	23.7

	Min	Max		Min	Max		Min	Max		Min	Max
Rottnest Island	19.5	27.3	Southern Cross	18.2	37.4	Southern Cross	18.7	36.1	Wandering	14.3	34.7
Jan 2010	19.5	27.2	Jan 2010	18.2	37.3	Feb 2010	18.6	36	Jan 2010	14.3	34.6

	Min	Max		Min	Max		Min	Max		Min	Max
Wandering	13.4	30.1	Wiluna	14.7	33.6	Wiluna	23.1	38.3	Wiluna	25.2	41.1
Mar 2010	13.4	29.9	Oct 2009	14.9	33.8	Dec 2009	23.1	38.1	Jan 2010	24.8	41.2

	Min	Max		Min	Max
Wyndham			York	16.5	36.7
	*	*	Jan 2010	16.5	36.6

* No change

		As originally posted on BOM website database

		As recorded on August 10 2010

When all the BOM adjustments are calibrated into my averages for the 12 months to July 2010, there is no change at all to the overall minimum and maximum averages ... i.e within adjustments by the BOM to its database since November to its monthly records since September 2009, the upward adjustments almost perfectly counter the downward adjustments. The consistency of adjustments made to January 2010 records suggests a database bug correction was again responsible for the "incorrect" original recording.

The increase in WA average temperatures coinciding with the month that a BOM database bug was corrected does not necessarily mean the Daily Weather Observations on the BOM website are inaccurate. It may well have been a very hot year across Western Australia.

However, the presence of software bugs for extended periods, as well as sporadic adjustments without a seeming pattern, raise questions about the reliability of data from the BOM website for research purposes.

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