Sunday 24 May 2020

Measures of rain at Mallacoota

I noticed on 23 May that the rainfall recorded at the BoM site for Mallacoota was a lot less each hour than I was recording at home.  Several members of the Mallacoota community provided me with their cumulative readings and they were very consistent with my readings.  I drove to some spots near the BoM site and the amount of water lying in ditches and the beach erosion by a small creek draining the area near the BoM site suggested to me that the BoM installation was well under-recordng the rain.

I was thus surprised to find that by early on 24 May the BoM had "caught up".  This led me to investigate the falls for various times and I find the BoM readings to be extremely strange.  I then included the readings from a wunderground site in the centre of Mallacoota under the name of Putz (the nickname of the site owner).  The location of the three sites is shown here.
A chart of the three series for the period 0100 hrs on 23 May to 0500 hrs on 24 May ....

... gives a very strange picture.  There is very close agreement between my Weather Station and Putz but the pattern shown by the BoM site is very different.  Were this during a period of thunderstorms or small intense rain cells I could understand the differences.  However this event was very staedy gentle rain over several hours.  Also the ground evidence of significant rain represented by the images linked above suggests the BoM record is well understated.

The final straw in the wind (straw in the rain?) is theat the wind direction through the day was consistently SW-WSW at my site so the weather was coming amost in a straight line from the BoM over Putz to my site!

I shall raise this with BoM.
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3 comments:

  1. Blair Trewin25 May 2020 at 12:58

    I've reported this to our observations people. It looks to me like a partially blocked gauge (past experience in places well endowed with wildlife is that often this turns out to be nesting birds).

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    Replies
    1. Flabmeister25 May 2020 at 13:25

      Thanks Blair. I suspect nesting birds a little unlikely at this time of year but Potter Wasps are a possibility.

      Delete
  2. Blair Trewin28 May 2020 at 15:06

    Have now confirmed that the gauge was blocked. Appears to be post-fire debris which presumably blew into the gauge intake. It's now been cleared.

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