Inconvenient facts about NT's Hot July

ABC's ineffectual reporters once again fail to ask any questions in regurgitating a BOM report on a hot July in the top end.
ABC's report identified the following key points:

Key points:

1. Some places saw temperatures between 3C and 4.5C above long-term average
2. In Darwin the overnight low only dropped below 20C six times
3. BOM says "hard to say if this is new normal"

Let's look at these one by one.

1. Some places saw temperatures between 3C and 4.5C above long-term average

ABC failed to question the BOM about the how the long term averages are currently determined. The changes quoted by BOM are based on the ACORN data. This is a manufactured dataset based on an undisclosed homogenisation algorithm with arbitrary adjustments (see below). For the NT it is derived from a handful of stations. The NT covers 1.421 million km²; over such a large area how useful is an average based on just a handful of homogenised stations? 

2. In Darwin the overnight low only dropped below 20C six times

So what! Based on the actual measurements from the Old Darwin Post Office (14016) and Airport (14015) this is not out of the ordinary and has been surpassed on quite a few occasions. It might have been worth the BOM pointing out that in 1915 NO (yes zero) nights dropped below 20C, and that there have been warmer overnight averages in Darwin the past (see tables below). ABC's reporter may have asked on how many occasions this had occurred previously and what was the record?

# nights below 20C-Selected months Darwin Post Office (BOM 14016) (More if you look).

1906:1

1915:0

1916:1

1917:2

1920:1

3. BOM says "hard to say if this is new normal"
As usual ABC (and BOM) omit any context or history in claims involving climate change. The graphs below show actual mean maximum and minimum temperatures for Darwin Post Office (BOM 14016) and Darwin Airport (14015) for July from the start of records in 1869. For the Post Office observations were collected in a Stevenson Screen from at least 1890. For the Darwin area this shows a cyclic pattern of temperature variation in both Min and Max means. Interestingly, based on the un-adjusted data there is little change in the long term means. Mean temperatures provide little information about weather experienced on a day by day basis. As usual ABC (and BOM's) reporting is superficial, omits key information and fails to inform.

Jennifer Marohasy has an informative post on homogenisation of Darwin's temperature record. See HERE.

Addendum
As an indication of the arbitrary nature of BOM's homogenisation process the list below shows recorded and ACORN minimum temperatures, and the difference for Darwin Post Office (14016) for July 1915. The range of adjustments over the period lack any credibility.

1915 (JULY)	RECORDED	ACORN	DIFF
1st	21.7	21.1	0.6
2nd	21.2	20.1	1.1
3rd	21.7	21.1	0.6
4th	21.8	21.2	0.6
5th	21.7	21.1	0.6
6th	21.8	21.2	0.6
7th	22.3	21.7	0.6
8th	23.1	22.3	0.8
9th	22.3	21.7	0.6
10th	21.4	20.5	0.9
11th	20.1	19.2	0.9
12th	21.4	20.5	0.9
13th	22.5	21.9	0.6
14th	23.3	22.5	0.8
15th	23.3	22.5	0.8
16th	23.8	23	0.8
17th	23.1	22.3	0.8
18th	21.7	21.1	0.6
19th	22.8	22.1	0.7
20th	23.2	22.4	0.8
21st	22.3	21.7	0.6
22nd	23.1	22.3	0.8
23rd	21.8	21.2	0.6
24th	21.1	20	1.1
25th	21.4	20.5	0.9
26th	21.8	21.2	0.6
27th	22.6	21.9	0.7
28th	23.1	22.3	0.8
29th	21.9	21.2	0.7
30th	22.2	21.6	0.6
31st	22.5	21.9	0.6