December 2017 as in 2016

Blooms of San Pedro Cactus at Manilla NSW

San Pedro Cactus 2017

The weather in this December was very like the weather a year ago. Even details were similar. Each had just one 40° day. Each had one night near 25°, about 9° above normal. This December had one hot spell 6.3° above normal: last December had two hot spells 4.8° and 3.6° above normal. Neither had cool spells.
This December’s highest rainfall reading, 15.5 mm (unofficial), was like last December’s 17.8 mm (also unofficial). This month had fewer rain days (5 vs. 12) and longer dry spells.

Weather log for December 2017

Comparing December months

This was one of the hottest Decembers in the new century. The mean daily maximum, at 33.7°, equals that of December 2005, but is beaten by 33.8° last December. The mean daily minimum, at 18.2°, equals that of last December, but is not as warm as the 18.6° of December 2009. By contrast, December 2011 was the coldest, with a mean maximum of only 27.0°, and a mean minimum of only 13.9°.
This month’s subsoil temperature (23.0°) was very cool; one of four December values more than a degree below normal.
Like last December, this month was not very moist, but not very sunny either.
The rainfall of 48.2 mm was practically the same as in December 2016 and 2013. It is at the 35th percentile: not high, but high enough to prevent shortages.

Climate in December months

The Year 2017 was warm and dry

In this record (2000 to 2017), Manilla’s average annual temperature this year (18.65°) shows it to be the third warmest, after 2014 (19.01°) and 2009 (18.85°). The coolest was 2008 (17.19°), which was also cool globally. (Apart from 2008, Manilla annual temperatures do not follow global temperatures closely: the hottest year globally (2016) was not a very warm year here.)
Like the previous two years, 2017 had night temperatures half a degree below the normal value. Day temperatures, which had been near normal in 2015 and 2016, became a degree warmer. This year’s subsoil temperature (19.80°) was cool, very much cooler than in 2013 (22.19°).

It was a year of very low rainfall: 517 mm, which is at the 20th percentile, and 135 mm below the average (652 mm). Three even lower rainfall totals have occurred in the last sixteen years: 366 mm in 2002 (2nd percentile), 495 mm in 2009 (16th percentile), and 447 mm in 2014 (8th percentile).
Manilla yearly rainfall history: four momentsThis unusually high ratio of very dry years agrees with other patterns seen in Manilla’s annual rainfall. That is, in the moments of the frequency distributions. Recently, Manilla’s annual rainfall has had (i) very high kurtosis, showing increased extremes (“fat tails”), and (ii) negative skewness, showing that these extremes are low extremes, not high extremes.

Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available, but it is not.  The gauge last reported on 24 September 2017.

All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

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