Weather Report January 2020

This has been a very difficult report to compile both from the view of having data to access and refraining from making excessive commentary on the data I have available.

A particular problem arose with the BoM site for Mallacoota not reporting for a total of 10 days, making it almost impossible to use that data for historical comparisons.  Fortunately my personal site kept running even though the console would have been running on batteries for 14 days.  Where at times my records appeared to conflict with those from the BoM sites at the airport and/or Gabo Island they proved very consistent with those from a private site in town which is linked to internet (as long as power is available!) and provides a better reflection of conditions in town than the airport site...

Clearly the month was very dry, with a storm on 20 January the only major fall.  Most of the month was relatively cool due to the smoke coverage keeping the sun off.  Late in the month this had the somewhat contrary "blanket effect" of holding the heat in giving very high minima.  Humidity was abut normal.  Wind strength was as expected although it was unusual to find a high proportion of the wind coming from ESE rather than nnw.

Rainfall

Pathetic.  A little more than last year, but still well below average.  The concentration of the fal into the storm on the 20th is clear in this chart.

The number of days with falls above 0.2mm was, at 9 days, surprisingly a little above average for the month.  (The average was taken from BoM  data since 1974 and excludes the period 1979 - 1984 inclusive where it was common to find the reading spanning several days.)

Temperatures

My usual overall measure of temperatures is the anomaly taken as the difference between the average for the reference period and the long term average.  That is made very difficult for this year as the BoM site was out of action for 10 days.  I thought of using Gabo Island as a proxy but that also failed to report for 5 days.  My conclusion to this was to calculate  the anomaly using the days for which the sites had a 2020 value available. 

 As well as calculating the anomaly I have plotted the recorded value for 2020 and the average for the day.  As Gabo has more days available I have shown that first.  Note that I truncated the vertical scale to show more clearly the comparison between the two series and not out of an IPA/Murdochian shokanorror desire to panic people.

Looking at the charts it is not surprising to find that the anomaly for Gabo (+1.3^oC) is greater than for Mallacoota (+0.2^oC).   I believe this can be attributed to the skies at Gabo being less opaquely smothered in smoke.  For an assessment of comparison with long-term trends (who said "Climate Change"?) I believe the value for Gabo is a more useful indicator than that for Mallacoota.

A second approach to overall temperatures is to look at the daily extremes through the month.  These data are from my Weather Station.

I was quite surprised at the fluctuations.

Maximum temperatures

The highest temperature recorded at my WS in the month (38.0^oC) was on the 31st while the BoM site got to 34.9 on the same day. I plotted the maxima at my WS against those available from BoM:

 As expected my WS readings are higher than the BoM data (exaggerated by the truncated scale) due to the sea breeze kicking in in the afternoon.  However I believe that the long term average data for the BoM site provides a useful background for comparison on current values and in the chart below the 2020 value is from my WS while the other 2 values are BoM.  (From March onwards the 2019 value will also be from my WS.)

Of course, for refuting the views of climate change denialists (if anyone still espouses such views after this Summer) the argument will always be mounted using only the more consistent information from BoM.

The other interesting aspect of maximum temperatures in Summer is that of heat-waves.  The BoM defines a Heat Wave as 3 consecutive days of significantly above average maximum temperatures.  Taking this to mean the long term average maximum plus 1 standard deviation gives the lower limit for a heat wave in January of 25.1^oC.  My indicator statistics is number of Heat Wave Days HWD in a month - that is counting the number of days that contribute to heat waves in the month.  For 2020 there were 8 such days (including the 30th and 31st (both over 25.1^oC as was the 1st of February)!

I shall do an analysis of the cut off temperatures for other months and thus a time series of HWDs.

Minimum temperatures

The month concluded with an extremely warm minimum on the 31st (BoM 22.9^oC, WS 23.1^oC).  The BoM reading was the 4th highest on record (stealing February's thunder: the value (24.0^oC) on 1st February equalled the all time high minmum for Mallacoota).

The BoM and WS values were very close.

 This year's average minimum was a bit above average but less so than 2019.

Humidity

The daily numbers especially for 1500 hrs, vary greatly though the month.  RH of close to 40% is very low for a coastal site.

 The morning value was higher than 2019 and the historic BoM average.

 The afternoon value was a touch under average and considerably below the value for 2019.

Wind

The average daily run was 137 km which is reasonably high when compared with other values for my WS.  The little data on wind published (at no cost) by BoM suggests it is of a broadly correct order of magnitude.

The wind rose is interesting in showing a high proportion of wind coming from the ESE, rather than the more usual NNW - N section of the rose.

An initial review suggests the wind mainly came from this direction for the period 17th to 29th.  The very hot weather of the 30th to 31st reflected a return to N winds.