Weather Report: December 2020

 In summary mild and damp(ish).  I come to that conclusion as the temperature anomaly was within 0.1C of the long term mean and the rainfall was 105% of the long term median.  WRT temperature the anomaly was basically a balance between above average minima (17 days) and below average maxima (23 days). 

I have included below some graphs showing how December 2020 was cooler and more humid than December 2019.

Rainfall

As noted in the preamble the fall (68 mm) was a little over median (65 mm) but a little under the mean (69 mm).  It was very much over the miserable 6 mm recorded in December 2019.

Clearly we had one major event (22nd -23rd) that accounted for most of the fall.

A chart of the time series of December rainfall shows how variable the falls are.  The upper bound of the 95% confidence interval is 152 mm which was exceeded in 2004 and 2018.  (The lower bound is below zero!)  Obviously there is no point trying to fit a trend to this.

C

Temperatures

My overall measure of the temperature - the anomaly - is the difference between the average temperature for the month and the long term mean monthly temperature.  For this I use only BoM data to avoid the biasing effect of my WS having warmer maxima than the BoM site.  Overall the month ended up with an anomaly of +0.09C, which I regard as being effectively zero.

As has been the case for most months in recent years, as noted in the preamble this outcome is the balance between above average minima and below average maxima.  

The daily extremes show a warm start to the month and a warm spell in the middle but overall mild temperatures.

Maximum temperatures

The average maximum temperature from my WS was slightly above the average (mainly BoM data) but very much below the value for 2019.  

In December 2019 we had 6 days above 30C (peaking at 40.1C on the 30th) while in 2020 the maximum was 29.1C.  (Setting the boundary as a maximum of 25C , that was exceeded on 13 days in 2019 but only 7 days in 2020.)

It is instructive to look at the daily maximum temperatures for December 2019 and 2020.  The build up of heat late in 2019 is clear.  (Note: these are from my WS: the BoM site became unreliable on the 31st as it recorded 60C (and 80 kph winds) when the firefront passed through the site.)

Minimum Temperatures

As indicated above the minima were generally above average: this applies to both the BoM data and my WS which are usually very close in this parameter.

Humidity

As would be expected for the number of days with a non-trivial rainfall the month seems to show quite high levels of humidity from both morning and afternoon readings, with very few readings below 50%

To look further into this I have plotted the average rH readings from my WS by hour for the month and compared it with the overall average values for each hour.  (This is possibly a tad daft, as humidities are higher in the colder months but it is difficult to get many readings form other sources.)  I was surprised to see that only the mid-day humidities were above "average'.

To get a better comparison I compared average hourly humidities for December 2019 and 2020.  Clearly 2020 was moister through the day.

The next two graphs give comparisons for the average rH at the standard humidity times of 0900 and 1500 hrs.  Both well above 2019 and the early time well above the historic BoM average as well.

Wind

Overall about an average month for wind.

On a daily basis the run recorded at home was particularly long on the 14th and 15th, giving the longest 2 day run I have recorded here.  Those two days stand out in a comparison with December 2019, but the rest of the month is not noteworthy.  I cannot work out how to get (without spending serious coin) daily runs from BoM.

The direction of the wind over the month was similar for hourly direction and gust.  The emphasis on wind from the ESE was typical for the month (as far as my limited data can suggest).