Seasonal Weather Report: Autumn 2018

For reasons explained in this post I think it is more helpful, for my interests, to depart from the standard astronomical definition of seasons.  Under my theory Autumn comprises the four months of March -June, so we have just finished the 2018 edition of that season, and this is a review of the total period.

Hopefully what I have to say will be able to be explained in terms of comments I made about the component months!

The story is very consistent across the season with the only exception being the relatively extremely high maximum temperatures in April.  Otherwise it it close to average maxima, above average minima and dry - both as regards rainfall and relative humidity.

Rainfall

All months refer to low levels of rainfall, and part of my commentary for June explains this has been a feature to at least 18 months, and possibly as much as 7 years.  NSW Local Land Services describe it as "a dry stretch" which is probably understatement!

For this Autumn we have recorded 80.2mm of rain to be contrasted with an average Autumnal fall (or possibly a Fall fall, if we feel like sucking up to the Land of The Donald) of 193.4mm.  The only drier Autumn, since our records began in 1985 was 2004 with 34.3mm.  2011 was also pretty arid with 85.8mm.  Here is a graph.
 This shows a frequency distribution with 'round' class boundaries.  Its probably good that the average falls in the largest group/

Temperatures

In compiling this post I gave some serious thought to the data for minimum temperatures and how they compared with the BoM data for Canberra (using Canberra Airport for values since 2010, and Canberra Airport Comparison site for previous years).  The conclusion I reached was that the strong trend upwards in the Carwoola data was not sustainable.  I have previously become doubtful about some of the Summer maximum temperatures recorded in the mid noughties. 

As a consequence I have decided that all my analysis from henceforth will be restricted to the years since 2010.  I shall retain a copy of the old data in case it becomes useful

Maximum temperatures

The average daily maximum temperature for the season was 18.8oC, well above the average value. since 2010, of 18.0oC.  It is also towards the upper end of the range from 16.8oC (in 2011) to 19.2oC (2013).

The long range chart shows a rather variable set of maximums with no significant trend.

Minimum Temperatures

In each month - for most of the last two years I have commented on the most obvious feature of the weather being the relatively high minimum temperatures.  However as a result of the investigations referred to in the preamble to the Temperature section I have concluded that the values for the earlier years are not comparable with those for later years.  Thus I resile from those comments.

I won't use your bandwidth by showing the dodgy data but do offer this chart comparing the Carwoola and BoM Airport data to support my belief that the data since 2010 is of good quality.


While not the highest seasonal minimum (5.88oC, in 2016) this year's  5.77 is the second highest.  There is no significant trend in either series.

Humidity

I only have 5 years of humidity data so it's difficult to make any large calls.  Basically every month was below average humidity at 1500Hrs so it is not surprising that the season in total was also below average.

I have just started to look at rH for 0900 hrs and have plotted below the seasonal averages for both times.
I was astonished at the similarity of shape of the 2 charts.  Not surprisingly the correlation coefficient between the two series was 0.995!

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