Putting Temperature in Context: Pt 2

To show how handy my Excel worksheet is, here’s one I did in the last 15 minutes.

Apparently Sydney has had its warmest December minimum on record at 27.1 C.  The record before that was Christmas Day, 1868 at 26.3C.

The following seven plots show this in context.

Fig. 1:  The annual range in Sydney’s minima:


Extremes in minima can occur any time between October and March.

Fig. 2:  The first 2 weeks of December


Plainly, a new record was set this morning, but apart from Day 340 the other days are within the normal range.

Fig. 3:  7 day mean of Tmin in this period


Extreme, but a number of previous years had warmer averages.

Fig. 4:  Consecutive days above 20C Tmin.


But there have been longer periods of warm minima in the past.

Now let’s look at the same metric, but for all of December.

Fig. 5:  All Decembers (including leap years).


A record for December, with 1868 in second place.

Fig. 6:  7 day mean of Tmin for Decembers


Seven day periods of warm nights are not new.  The horizontal black line shows the average to this morning (20.6C) is matched or exceeded by a dozen other Decembers.  (Of course this December isn’t half way through yet.)  Also note what appears to be a step change about 1970.

Fig. 7:  Consecutive days above 20C Tmin in December.


I doubt if 15 December will be as warm as today, but could still be over 20C.

This is weather, not global warming.



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5 Responses to “Putting Temperature in Context: Pt 2”

  1. waclimate Says:

    Sydney’s maxima heatwave was two days at 37.8C and 37.2C. Sydney Observatory’s hottest ever December day was 42.2C in 1957.

    I think the record minima of 27.1C at the observatory should be seen in the context of UHI.

    Other record hotspots were Sydney Airport and Parramatta North, both at 27.5C. The nearest weather station to Sydney Airport is Canterbury Racecourse, about halfway between the latitude of the observatory and airport, where the min was 23.0C, which was 4.5C cooler.

    Sydney Harbour 66196 was 22.3C and Newcastle Nobbys AWS was 23.1C.

    On the coast north of Sydney at Gosford AWS the min was 20.9C and to the south at Bellambi AWS it was 22.0C. As far west possible before the mountains at Penrith, the overnight min was 21.8C.

    The min in certain parts of central Sydney were 6C to 7C warmer than districts north, south and west of the city.

    The validity of Sydney’s record December daily min is questionable when the environment has changed since 1868 to now be a carpet of concrete, bitumen and a major international airport.

    • kenskingdom Says:

      “The validity of Sydney’s record December daily min is questionable when the environment has changed since 1868 to now be a carpet of concrete, bitumen and a major international airport.”

      Absolutely true.

  2. Macha Says:

    Plus, the great climate shift of 1978/79….

  3. Brad Wrightson Says:

    Thanks again Ken.

  4. Andrew Says:

    And don’t forget that the former record on “Christmas Day, 1868” probably doesn’t count because it predates the weather bureau and the “official” records. It should count of course. But like the federation drought and the melbourne heat wave of 1908 difficult details like this have been expunged from the debate.

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