Friday, 4 October 2013

September weather

So here we are in Spring!

The most dominant features of the weather this month have been:
  • a torrential downpour for just about all of the 17th of the month; and
  • very unpleasant winds in the latter half.
Largely as a result of the drenching referred to above we got the most rain of any September since we have lived here.  Obviously way above average.
This second Chart shows the concentration of the rain in the middle of the month.
We recorded 0.2mm on the 26th, giving 6 rain-days in total.

I am using Maximum gust as my indicator of "windiness".  My weather station is mounted about 15m above the ground and on a hillside with an Easterly aspect  so it doesn't get the full blast of the gale.  However I think it provides a relative measure of the breeze.  This chart shows the maximum daily gusts for September on its own.  (I also looked at the average daily maximum gust and it gave pretty much the same picture, so will stick with the simpler approach.)
Looking at the average of maximum gusts September scored 19.7km/hr while August was 17.4.  The broad picture of daily maximum gust for the two months reflects September - particularly the second half -  being draughtier.
I will conclude the wind section, not with an oboe concerto but a couple of BoM doppler radar images.  These show the speed of the wind relative to the point at which the observations are taken, which in this case is the Captains Flat radar tower.  
  • The first image is from 16 September and is included because of the line across the chart from W to NE.  South and East of that line there are very strong Easterly winds: NW of that line there are light NW winds.  I'd suggest a flight through that line would have been a bit bumpy! 
  • There wasn't much rain around on the 25th, mainly verga.  Thus the reflections weren't so strong.  However note the flecks of deep red over Belconnen.  The radar system 'cycles' presentation colours so if it gets above the range for deep blue it starts again on red showing  that the wind was above 100kph!

The middle of the month was marked by some rather ordinary maxima and almost non-existent ranges of temperature, but overall I think we are getting out of Winter.  The small table below shows that the maxima are increasing and the number of frosts, both ground and air, are dropping significantly.

July  August September
Days max below 10 6 8 0
Days max above 15 1 7 25
Days max above 20 10
Days min below 0 14 10 5
Days min below 2 21 19 10
Days range <10 nbsp="" p="">13 13 5
Basically quite steady humidity (as measured by 5pm relative humidity), apart from the rain period in the middle of the month.

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