Minus 10.4 degrees C was recorded originally at GOULBURN AIRPORT AWS (070330) which was filed by blogger Lance who noticed the BoM rapidly altered this to -10. Jennifer Marohasy blogged on the issue 4 July and passed the info on to a journalist who asked the BoM if they could explain. BoM said they have a “QC” auto function clipping off extremes in case there are errors. And this caused the reset to -10°. JM blogs again on 5 July. This revelation of raw data trimmimg is brand new to many of us who monitor BoM data – but OK thats what the BoM says happened. Jo Nova is also onto the issue. Lance and I checked BoM AWAP maps for NSW daily minimum temperature and noticed the contouring was hugely in error when checked against actual minimums. I have NSW daily minimum temperature maps offline for the 1st July – 2nd July and 3rd July. Just looking at data from the Southern Tablelands region (the white O circles the Goulburn and Canberra localities.) Goulburn is in the wrong contour zone all 3 days. Canberra Airport should be well into the -6 to -9 zone on all 3 days – yet it is always plotted on the boundary of the -3 to -6 and -6 to -9 zones. Always wrong. Taralga about 40km NNE of Goulburn (approx marked white T) read -7° on the 1st & 2nd yet the correct -6 to -9 degrees zone boundary is way too far west on those days. Yass recorded -8.7 on the 2nd yet the contouring has Yass in the next warmer zone. Likewise Cooma on the 3rd should be in the -6 to -9 zone but is shown in the next warmer zone. I expect readers might find errors in other parts of the State – or in other States
With so many errors I wonder what purpose these maps can be fit for. On the issue of the BoM clipping sub -10° readings back to an even -10. Lance mentioned to me these very cold reading from Goulburn Aero Club 70210 in July 1971 – down to -13.9°. Cop that 14 days of frosts in 1971!! Worth noting too the all time coldest Canberra Airport min was -10 on 11 Jul 1971. So setting -10 as an alarm was somewhat odd and without sound scientific foundations – but Hey!! it is the BoM.
Thanks for raising the issue of the contour maps. What a tangled web they weave.
See this?
principia-scientific.org/breaking-fatal-courtroom-act-ruins-michael-hockey-stick-mann/
Pat at the Jo Nova blog links to this.
“It does appear that warmer than normal days will arrive by the end of July and continue into August and may last into September. I do wonder about the accuracy of AWS stations. Last Saturday whilst in Cobar the AWS station recorded minus 0.6. The MO station run manually recorded minus 5.5.
When I came outside in the early morning my car was coated with thick ice and my push bike parked nearby had a coating of ice on the frame. The MO reading is obviously more correct.
Some AWS stations have lost some recordings due to technical failures and there has been no backup to recover lost readings.”
www.countrynews.com.au/2017/07/03/5681/several-record-low-july-temperatures-recorded
Lance Pidgeon
It’s common to have ground frost when air temps stay above zero. The ground radiates heat, while the air doesn’t (much). We see it occasionally in Perth. Car windscreens are particularly prone to ice formation.
That article you linked to Siliggy got the Cobar temperatures wrong way around for the 1st July.
The Airport AWS read -5.5 while the MO on north edge town close to housing was much warmer at only -0.6.
www.australianweathernews.com/data/DS1_48.HTM
Once they start altering raw temperature readings, all historical comparisons are meaningless.
Think of all the work the BoM put into ACORN and its predecessors to homogenise data. In all those contortionist adjustments, I don’t remember seeing any for the effects of “quality control” (QC) just chopping off extreme values. So chalk up yet another fault in ACORN.
And what have they done with historical “raw” temperatures? If it had been minus 10.4 in Goulburn 50 years ago, would they have let that stand? Seems the answer is probably yes from the fact that they have a minus 13.9 still showing in 1971.
Furthermore, what about record high temperatures? They never seem to chop them back. No doubt their models tell them that global warming means they are OK…
Beachgirl The Cobar story is getting even more interesting at a rate faster than I can type. For example. “Staff cut as weather Station goes fully automatic” cobarweekly.com.au/?p=2707
And both of them appear here. So the claim that one of them is manual is also perhaps false or not the same as the automatic report from the same site.
Ooops here. www.bom.gov.au/nsw/observations/nswall.shtml
Remember when the BoM increased the scale on their maps to 54 degrees ? – here is an article – one of many – I wonder if this clipping of “extremes” came in at that time?
Temperatures off the charts as Australia turns deep purple 8 Jan 2013
www.smh.com.au/environment/weather/temperatures-off-the-charts-as-australia-turns-deep-purple-20130108-2ce33.html
Forecast maps up to 54°
www.bom.gov.au/australia/charts/viewer/index.shtml?type=T&level=2m&tz=AEDT&area=Au&model=CG&chartSubmit=Refresh+View
I suspect the rounding down of extremes is justified by the lack of precision of manually read min/max thermometers, in comparison with the electronic thermometers in use today. I recall reading that was done in the USA.
If you fiddle with the data enough, you will find what you are looking for. It’s called Confirmation Bias.
More about Cobar on the July 1. The AWS site was 8.7 degrees below the long term Mean of 3.2 at that site.
This map should show the second shade of blue there not the first. www.bom.gov.au/web03/ncc/www/awap/temperature/minanom/daily/colour/history/ns/2017070120170701.hres.gif
The MO site was 5.7 degrees below the long term Mean of 5.1 at that site. So it SHOULD be the first shade of blue. The line of shade change should pass between them.
My big question is. Are the national averages calculated from the same database that produces these maps? If so the minimum trend will be calculated to show erroneously higher than it should. This is important because for the greenhouse gas theories to be correct minimums need to be seen to warm FASTER than maximums.
Moss Vale 01.07.2017
top temp 9.1, BOM records 9.6
Why? this seems to happen a bit…
www.weatherzone.com.au/station.jsp?lt=site&lc=68239&dt=01%2F07%2F2017