July 2023 Weather report

 In summary, and not surprising anyone, a very dry and quite warm month.

Rainfall

What is this thing called rain?  Our fall this month at Angophora Drive totalled 7.2 mm, of which 14% (ie a total of 1mm) came in 'falls' of 0.2mm, which is a heavy dew rather than rain.  This is shown- almost by omission in the chart.

The next chart shows the declining value of a pro-rata estimate of annual fall for 2023.  The last "local peak" of significance was 9 May: in simple words we haven't had significant rain for nearly 2 months.

In terms of history there have been 13 months since 1983 with less rain.  

Other local stations have recorded similar miserable totals: BoM Airport 8.6mm and Gabo Island 8.0mm.  Looking upstream, the BoM station Bombala AWS - very close to the source of the Genoa River - has recorded 6.2mm, with the only fall >0.4m being 3.6mm on 5 July.

Temperature

The average temperature for the month was 0.96C above the long term average for July.  A chart of the development of this metric (the anomaly) shows it to have been in the range +0.5 - +1C for most of the month with a slightly warmer period in mid July.

Since I have started calculating the anomaly (February 2019) I have 49 readings of which 32 have been positive, suggesting a warming period.  There were breaks in the series prior to February 2020 so the time series chart starts in that month.  

The raw data fluctuates greatly, but the 12 month moving average removes the noise attributable to seasonality, showing a gradual decline.  I need to think a little more about the interpretation of these contradictory results.  A first thought is that this period includes:

• the end of a drought;
• at least 2 years of a La Nina event; and
• the start of an El Nino ....

... so it it is really impossible to make any generalisations from such a short series.

The series of the temperature extremes for the month is below.  I'll comment on the two series in the subsections below.  But I will note that we didn't light our fire for the last 4 days of the month, while from the 19th to the 21st we were lighting it around noon rather than mid afternoon.

Minimum temperatures

The average minimum temperature for July 2023 (6.83C) was above the mean value, but below the value for July 2022.

The next chart shows the average monthly temperatures recorded on my weather station since we moved here.   In essence all 5 series are quite well bunched.

Taking a longer view, and including the data from BoM at the airport for years prior to 2019, shows a highly variable series.  While the trend line does slope upwards the value of r2 shows this to be not significant.

I have also looked at how the daily values for minimum temperature compare with the long term average minimum for the month.  7 of the values - mainly early in the month - were more than 1 standard deviation above the long term mean.  3 values, spread through the second half of the month, were more than 1 standard deviation below the long term mean.  One of the significantly low values coincided with a significantly low maximum: I term this a Cold Day!

Maximum temperatures

Note that the years before 2019 are based on BoM data but adjusted to overcome the cooling effect of afternoon sea breezes so that they are more comparable with readings from my WS.  

The average maximum temperature for July 2023 (16.9C) was very much higher than for both July 2022 and the mean July average maximum (if that makes sense).  It was the highest average maximum for any July since my series began in 1993.

For the WS maximum series the bunching effect is not so great as for the minimum series shown above.  The series for 2023 in particular varies from below average to above average more than other years: possibly this is an effect of switching from La Nina to El Nino?

The time series for maxima is all over the place.

Looking a the individual maxima compared to the long term July average the most notable feature is the 9 days, mainly late in the month, in which the observed temperature was more than 1 SD above the mean.  Indeed, of the last 5 days of the month 4 were greater than 2 SD above the mean. Those 4 days were all in the top 30 (0.5% of 1519) maxima in the series).

However there were also a few very low maxima.  3 readings (19th to 21st) were all more than 1 SD below the long term monthly average.

Humidity

There are some very low readings in that chart.  They are associated with periods of North-Easterly wind and examining the whole sequence of times show a gradual decrease in humidity followed by a gradual increase once the wind swings back to more Southerly.  So I believe it shows reality.

A comparison with July of the 4 previous years is a little strange as for both standard times 2 years have a high value and 2 years a low value.  For both standard times 2023 is almost identical to the low values.  I am unsure what this means but believe the data to be fair quality.

Wind

With an average run of 66km the month was quite calm.  Only 6 days had runs of 100km or more.  This was a very low level f wind even for the least windy part of the year.

TEMPEST data

In addition to the data from my weather station a friend, located in the town centre, has provided access to data from his weather station connected to the TEMPEST network.  The broad picture provided fordata items in common with my WS for July is very similar to that discussed above.  

In addition TEMPEST gives information of solar radiation and lightning strikes amongst other data.  As I only have a few months readings limited analysis is possible, but watch this space (or rather, future editions of this space).

The lightning strike data counts strikes within a 40 km radius of the station.  I have used Google Earth to map the extent of this range.  (My brain is slightly boggled as to how the system does this!)