Australia’s Wacky Weather Station Comparison 2: Wagin (WA)

After surveying 666 weather stations across Australia and finding nearly half (49.25%) are not compliant with Bureau of Meteorology siting specifications, in this series of posts I compare daily temperature data from pairs of compliant and non-compliant stations. Here’s the first in this series.

Wagin and Katanning

These stations are about 200km south-east of Perth.

Fig. 1:  Wagin map location per Google Maps

Katanning is in a paddock 48.7km south-east of Wagin.

Fig.2:  Wagin and Katanning

Wagin 10647 is in the middle of a small town. The screen has a bare dirt path leading to it. It is 10 metres from a bitumen street. A colourbond fence is to the north-east and an 18 metre tree is less than 20 metres away. More trees are to the south.

Fig. 3:  Wagin (Google satellite image 2019)

Katanning 10916 is in an open rural setting, on a slope as the 2013 site plan shows:

Fig. 4:  Katanning site plan 2013

Fig. 5:  Katanning (Google satellite image 2020)

Katanning is 64 metres higher than Wagin, but the surrounding country is similar- dry, flat or gently sloping.  Again, an important difference is that Wagin is a manual station with liquid-in-glass thermometers, while Katanning is an Automatic Weather Station (installed 1998) with an electronic temperature probe transmitting data every minute.

If we plot all daily maxima from 2010 to 2019 for Katanning against Wagin, we see that temperatures match quite closely:

Fig. 6:  Tmax at Katanning as a function of Tmax at Wagin

The trend equation shows Katanning is on average more than 0.5C cooler than Wagin. A time series of the 31 day centred mean of the daily difference between them shows more detail:

Fig. 7:  31 day mean daily difference Wagin minus Katanning Tmax

Values above zero mean Wagin is warmer than Katanning; below zero, Wagin is cooler.  Note that apart from a brief episode in 2012, Wagin is always warmer than Katanning.

This is a plot of mean differences by month:

Fig. 8: 31 day mean daily difference Wagin minus Katanning Tmax by month

Wagin is warmer in every month- apart from a three month period in 2012 which shows in the black ellipse.

Minimum temperatures don’t match as closely…

Fig. 9:  Tmin at Katanning as a function of Tmin at Wagin

Fig. 10:  31 day mean daily difference Wagin minus Katanning Tmin

Wagin is warmer in summer but cooler in winter. Possibly, due to the sloping ground at Katanning, cold air flows downhill away from the screen in cool months, keeping recorded minima higher than in Wagin.

Fig. 11: 31 day mean daily difference Wagin minus Katanning Tmin by month

A note on accuracy:

The centred 31 day running correlation is useful for detecting inconsistencies.

Fig. 12:  Centred  31 day running correlation between Wagin and Katanning maxima

Fig. 13:  Centred  31 day running correlation between Wagin and Katanning minima

Although there are a couple of obvious inconsistencies in maxima, the correlation in minima has been much worse every year.

Fig. 14:  Daily difference in maxima

There are examples of up to 6 degrees difference on some days, and some much larger, possibly due to observation or recording error- for example, by recording temperature on the wrong day, or recording 19.6 instead of 29.6.

In recent years, Wagin 10647, a manual station that does not comply with site specifications, has warmer maxima than its compliant neighbour Katanning 10916 all year round, and has warmer minima in summers. 

In this example, siting non-compliance has a large effect on temperature.

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One Response to “Australia’s Wacky Weather Station Comparison 2: Wagin (WA)”

  1. www.speed79.com Says:

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    Australia’s Wacky Weather Station Comparison 2: Wagin (WA) | kenskingdom

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