BoM fiddling Goulburn minimum temperature 2nd July 2017 reveals extent of errors in BoM AWAP temperature maps

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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 they 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°. So setting -10 as an alarm was somewhat odd and without sound scientific foundations – but Hey!! it is the BoM.

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July 5, 2017 at 10:35PM