July Weather Report

You may have noticed that the weather was a little damp this month.  It was also quite mild.  This report may be quite brief as Blogger seemed to have an HTML cow with my first attempt and I am not sure how I will go on recovering it.  (It seems to have worked OK.  No idea what the problem was but Blogger has been updated to appear better on mobile phones and as usual that has mucked up stuff on computers.  And Google seems unwilling to listen to such heresy.)

Rainfall

A very wet month at Mallacoota. We totaled 170 mm at home.   A very significant amount above the median and 2019. The Airport managed 151 mm: the sixth highest July reading (out of 42) at the current site.

We experienced 2 significant rain events during the month.  The first, from the 12th to the 16th, amounted to 52 mm. The second, from the 26th to the 31st, brought 105.4 mm

In terms of impact on the water level in the Inlet the falls in the hinterland are also important.   There seems to be no weather station actually in the Mallacoota Inlet Catchment (including both Genoa and Wallaraugh Rivers) which provides time series data.   However the BoM station Bombala AWS, while situated in the Snowy River catchment, is not far from the upper catchment of the Genoa River and seems to serve as an indicator of upstream falls   At that site the falls in the first event were approximately double those of Mallacoota sites while the opposite applies for the second event.

Only short term data for the flood level gauge at the Genoa River is available from the BoM site on line.   What is available at the time of posting (1 August) shows the River at~2.4m, which is above minor flood level, on 28 July but dropping to 1.12 m by the end of the month

The impact of the rainfall from the 2 events is clearly shown in a chart of the heights at the official gauge at Mallacoota Wharf.   Following the opening of the Mouth readings here are influenced greatly by the tide and if the wind is pushing ocean water into the Inlet.   However the impact of the flood peak in elevating water levels on 28 July is very clear.

Compiling a prorata estimate of the annual rainfall shows a nice uptick this month with the estimate at the end of the month at an annual total of 957 mm.

Temperature

The overall picture was above average minimum temperatures and below average maximum temperatures.   That combination of extremes occurred on 18 of 31 days in contrast to the expected occurrence of 7 days.   This can be expressed by the anomaly (current average-long term average) on +0.68C.  The progress of the anomaly through the month is illustrated in this chart.

My second overall view of temperature is the daily extremes.   Fairly bland with no runs of unduly hot or cold.

Maximum Temperatures

The average maximum temperature (15.27C) was a little above average but a fair bit below last years average maximum.   The latter is almost certainly due to this year being very wet and thus cloudy while last year was a tad arid.

The average monthly maximum series is a bit bouncy but the linear trend line is well below the level of significance

I am noticing that the average maxima I am generating at home are quite consistently a degree or so above those at the airport.   This is quite readily explained by the impact of afternoon sea breezes cooling the airport more than here,   I shall research this a little more and probably adjust my historical series.   Expect an ad hoc post in the near future.

Minimum Temperatures

Quite a warm month overall for average minimum (7.89C), as a result of the cloud blanket!   Also I expect to find a much higher proportion of the wind reading coming from the sea rather than the land.

The trend line for the minimum time series is a close to flat as could be expected.   I shall check the comparison with the BoM data but for this month at least they are in close agreement.

Humidity

A large amount of rain is - possibly by definition - associated with high humidity,   And so it was this year.   The two periods of heavy rain are identifiable as the days on which the 0900 and 1500 humidities are close to identical.

For both time periods the 2020 value is well above the 2019 and longer term average values.

Wind

The month was quite moderate for wind.   The day (13th) with the longest run (246 km) was the 31st longest run of the 536 days in my records.   Overall the run was a little less than last year and a fair amount less than my long term indicator.   (Note that home is a lot less windy than the BoM site so I have adjusted the BoM data.   A crude adjustment but in this case I have little other data to go on.)

In terms of the direction of the wind the rose shows that a very high proportion of the wind came from the Western half of the compass.

In an earlier post about the heavy rain event of 26 -30 July I showed how once the low actually arrived the wind settled down to blow from the ESE (with occasional strong gusts from the NW as mini-cells came through).  A similar pattern was also evident in the first wet period.  I haven't been able to work out how to show that in a graph but, trust me, nearly all the wind from the Eastern half of the compass came from the core days of those systems.