Sunday, 3 April 2016

Weather Report March 2016

My gut feeling is that it was a relatively mild month with sort-of acceptable rain.  Certainly Autumn arrived sometime during the month.  I'll finish by reviewing this ominous statement.

Rainfall

We totalled 48.8mm for the month which isn't too bad.  It is well over the miserable amount in March 2015 and about 10mm below the 9 year average.
 On looking at the yearly records the standout year for March was 2012 when we received 220mm (the highest monthly total I have recorded).   Removing that from the average, reduces that mean by ~20mm and makes March 2016 10mm above (adjusted) average!
The most notable aspect of the rain, as with other months this year, is that it has mainly just gone into the topsoil.  There has been very little flow in Whiskers Creek, apart from a massive flood on 3 March.  By 12 March the Creek had stopped flowing again and only got to trace level after 12mm on 18 March.  It has now stopped running again.

Temperature

I'll let a picture tell the story first:
The green bars show the range of temperature over the day while a red box shows the temperature was higher at 2330 than 0030 and a blue box shows a drop over the day.  My interpretation is that the temperature gradually warmed from 2nd to 8th of the month and then dropped from 14th to 23rd.  However the most interesting comparison is looking at the averages from 1st to 17th with those from the 18th to 31st.



max min
1st to 17th 30.09 13.55
18th to 31st 22.52   9.40

Comparing average maximum temperature for March 2016 with earlier years shows 2016 to be well above both 2015 and the 4 year average.
Similarly the average minimum temperature is well above the longer term average for the month and 4 degrees above the average minimum for 2015.

Humidity

As usual I have examined the external humidity at 3pm each day.
I have taken 40% as a "reasonable"the  level of humidity and it is interesting that this level, for a reading at 3pm, was not achieved until 10 March.  Thereafter the level fluctuates a lot, but is rarely below 40%!

My attention was gripped by the low level for March 3, when we recorded 20mm of rain.  Here is a graph of hour by hour humidity readings for that day also showing the rain  by 30 minute periods.
The unsurprising conclusion is that it gets humid and then rains (after which it remains humid).  It is interesting that, according to a neighbour's observation, the flood occurred quite soon after 6pm, or just after the heavy rainfall.  This strengthens my view that a logjam had blocked the Creek and it was that breaking which caused the flood.

Looking at the longer term comparison March 2016 was a bit more humid than 2015 but below the 4 year average for March.

Wind

This is a slightly vexed issue this month as a couple of days have very low readings - one day showing a maximum gust of 0kph.  This is more obviously than usual for wind readings (due to the positioning of the weather station) rubbish and I believe reflects a build up of cobwebs jamming the anenometer.  To overcome this I estimated the values for the affected days to give this graph.
Clearly there was a very above average windy day on 18 March!  Notwithstanding the dodginess of the values for a couple of days a graph of averages has been calculated.
A relatively calm month compared to last year and the long term average.

Profile of a Day.

I have looked at the wind for 18 March in comparison with the humidity.  (Note that I have divided the value of rH by 2 to fit it on the same scale as the wind).
Obviously a storm was coming as the humidity stayed very high until the peak wind gust arrived.  I also looked at the gust in comparison to the rainfall.  (Again I have fiddled with the value of the rain - multiplied by 10 - to fit the scale.)
In this case the rain started as the leading edge of the front arrived at about 8am.  I'd suggest a storm band was embedded in the front, arriving around 1:30pm giving a burst of rain and leading into the main gust of wind about 2:30pm.

Temperatures were fairly steady through the day but as mentioned in the temperature section above this marked the border between Summer and Autumn.

Expectations revisited

The first half of the month was hot, rather than mild, and as a result the statistics for the month suggest a warm spell.  Autumn arrived with a strong front and more rain on 18 March.

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