Tuesday, 2 February 2016

Weather report: January 2016 and 2015 Summary

The year 2016 started off rather hot and rapidly switched to wet!  I shall approach this report thematically covering, for each topic, details for January 2016, how that fits in with some monthly averages and how totals for 2015 compare with other years.

Rainfall.

The month began rather dryly continuing the El Nino theme from late 2015 and then switched to La Vieja.  The usual term is La Nina which only changes sex- this was such a switch I believe it needs to change age and sex, going from 'the boy child' to 'the old woman'.  A Uruguayan friend added the word "Regonzonda" to make "old hag" but we haven't got that wet yet. We ended up with 103mm for the month making it the second wettest January we have recorded in the 10 Januaries we have been here.
 Here are the daily totals 
This next chart shows the maximum rain rate, in millimetres/hour recorded each day.
The highest value I have recorded here in the last 3 years has been 174mm/hour.  However that was very extreme and the rates recorded here were the 7th highest (on the 21st) and 10th highest on the 30th.  The event on the 30th was a very serious and severe storm causing much damage in Forbes Creek, which is only 13km East of here.

Total rainfall by year

Total annual rainfall for 2015 was 641mm, well below the 9 year average of 707mm.  This is essentially an outcome of balancing 3 months with the highest monthly rainfall with 4 months of very low rainfall, including 2 "lowest recorded".  Here is a chart of annual rainfalls.

Temperature

The basic pattern for the month was a series of heating and cooling cycles.
We recorded 13 maxima over 30oC and 4 less than 20oC.  A delight of our climate is that it usually cools down overnight so 5 minima >15oC were unpleasant while the 7 less than 10oC were very welcome.  Overall I'd say it was a Summery month.

Looking at the monthly averages, the average maximum was a tad higher than last year but below the 4 year average.  

The average minimum was a bit lower than last year but above the long term average.

Average temperature over years

I have two years with full records of temperatures.  For 2014 the average of all hourly readings was 12.31oC while 2015 was slightly warmer at 12.70oC.  Obviously it is impossible to make any sensible comment about the significance of that comparison.  There are other ways of looking at the comparison, but the sample is really too small.

Humidity

As usual the 1500 relative humidity goes up and down a lot, with the high readings coming on rainy days.  This is not rocket science!  
 I have added a line for the 6am rH to the chart, which shows that the reading is typically over 90%, even in Summer.  The days when the 6am reading is low appear to be in front of a rain period, where the weather is coming from the West: that gives winds from the NW which have typical come across the dry centre of the Continent.  The exception is on the 29th- 30th, where the rain came down from the moist North.

In terms of longer term average January 2016 was well above 4 year average for the month but a little below last year.

Annual average value of 1500Hrs Humidity

As with temperature there are only 2 years to work with so I will just note that the value for 2014 was  was 52.4% and that for 2015 slightly higher at 53.8%. 

Wind

As always the wind gust data is very variable through the month. Most of the high speed gusts seem to precede rainy days (although we obviously had nothing like the storm which went through Forbes Creek Linked above).
Looking at averages the average gust speed for January was well below the avergae for this month, but still above some other monthly readings.




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