Draft March 2019 Weather report

I have called this a draft weather report as I have had a small computing disaster which means that I don't have access to a bunch of data I had previously compiled.  I hope this will be recovered in the nearish future at which point some of the material which follows may be augmented.  However, what's here should give some idea of what went on, and how it fits into history.

The material relating to the current month will, unless otherwise stated, be based on readings from my weather station (a Davis Vantage Vue on Angophora Drive, Mallacoota).  As that has only been functional for 6 weeks material comparing this month with longer term data will largely be based upon BoM data for Mallacoota, collected from a site near the Airport.

Overall Summary

The month was basically quite warm, with both average maximum and average minimum above the long term averages for the month.  

With a few very damp days rainfall is also above average, bringing the rainfall year to end of March (195 mm) close to the long term average (200 mm).

There were a few pretty windy days.  However the BoM average maximum daily gust came in at 40.0 kph compared with ~41 kph for March 2018 (as assessed by eyeballing a graph in the report for February 2019) - so probably about normal.

For relative humidity the 0900 hrs rH for this year was a little higher than last year (also from eyeballing a graph) while the 1500 hrs value at 69% was much higher than last year.  This probably reflects the rather low rainfall of last year.  A separate page on the BoM site confirms the average value for 0900 hrs close to 70% and shows the average 1500 hrs rH  is 66% - so again very close to normal.  The humidity data for my site is very similar to the BoM material.

On to the details.

Rainfall

As noted above the rainfall - as reported at the BoM site - was above the long term average.  It was also greatly above last year's miserable effort!  It brings the year-t-date value to within 5mm of the average fall to end March

The mean annual rainfall, since 1985,  at the BoM site is 935 mm.  Doing a pro-rata extrapolation of this suggests the total fall for 2019 will be close to 910mm  

Rain at home was about 13 mm greater than at the BoM site.  This can be expected when the falls are mainly due to thunderstorms.  It is a tad difficult to reconcile the two series as BoM (for reasons of historical consistency) use days ending at 0900 whereas I (for reasons of ease of compilation and common sense) use a day ending at 2400.  That being said here are the daily falls.

Temperatures

An overall comment on temperatures is that the monthly mean temperatures compare well between my site and the BoM site.

Generally the daily values are similar (within 3%) except where a cool change comes through early in the day.  That allows my maximum temperature for the day to be recorded early in the morning which may be well in excess of the BoM maximum recorded after 0900.  As the correlation coefficient is 0.94 the pattern across the month is still quite similar. Restricting my observations to those after 0900 gives a higher correlation coefficient of 0.98.

Maximum temperatures

The first chart compares BoM data on average maximums for this year. last year, and all years since 1995  While the month was above average, it was not as hot as 2018.

Looking at data for my site for 2019  shows a hot start to the month before settling down to a fairly stable middle of the month and a cooler last few days.

I have managed to chart when each day's maximum was recorded.  Usually in the afternoon but the two days with cold fronts stand out rather well!

Minimum Temperatures

Again begin with data for the BoM site.  In this case the minima average out to be well above both average and last year.  

 The daily values show very warm minima early in the month and, after a cool period, later in the month before finishing with some lower temperatures,

Most of the minima are expected between 0400 and 0800 but a few occurred late in the evening, presumably as a cool change arrives.

Average temperatures

Two measures of the mean temperature are available:

• For the BoM series it it the mean of the daily maximum and minimum; 
• For my own series it is possible to take the average of the 24 hourly readings.

As is clear from the graph the pattern between the two series s very consistent (correlation coefficient 0.98).

A main use of the average is to calculate the temperature anomaly which is the difference between the average for the current period and the long term average.  For March this comes to +1.2C, so a bit warmer than average.

Humidity

On comparing the BoM average values for the month with the long term averages given on the BoM site they are very similar.  Most comments are given in the preamble so here is a chart of daily values for home, for the two standard times.

The most surprising feature is that they are relatively close,  For Carwoola, which is much more inland  the 3pm rH is usually much lower.
Wind

I have taken my standard measure of windiness as the maximum daily gust.  BoM do not publish that measure as a long term average.  They do publish the averages for 0900 and 1500 speeds and in both cases the speeds for 2019 were below average.

I have compiled a chart of maximum daily gusts for the month for my system.

The 61kph blast on the 29th was impressive!

I have compiled a wind rosette in which the width of the segments reflects the number of readings from that direction.  There were no readings from the East or South, and the labels are a mess from ESE to SW!