Sunday, 1 January 2017

Weather report for December 2016

Here is the summary report to appear in the Gazette:
I shall try to do a review of 2016 as a whole in the near future.  In the meantime these notes will focus on the month of December.

For most of the variables I cover the month was pretty close to normal.  The exception to this was minimum temperature which was very much above average.  I think this explains why the second half of the month felt so hot.


We basically had four periods of rain through the month.  This ended up giving us close to average rainfall for the month, but well above last December's miserable effort!
Whiskers Creek was a bit reluctant to run , reflecting the soil being pretty dry, and well covered with vegetation both tending towards low run off.


My subjective feeling was that December was a hot month.  This may be influenced by 10 of the last 12 days getting over 30oC. The daily maxima are the top of the green lines!
A long warming trend is evident from the 10th to the 28th (red boxes, showing it was warmer at 2300 than at 0100).

Looking at the longer term the maximum temperature averaged out pretty much on the average (and similar to last year).
The next chart, of minimum temperatures, shows clearly that the issue was that the heat didn't dissipate at night.
 Looking at the data back to 1993 this is the highest average minimum we have recorded in the Carwoola area.  Looking at the 2016 value compared to other years the 2016 value is on average 2.3oC higher than other years.  (The range is from ~0.4oC higher in a few years  to ~6.0oC higher in the mid 90s.)

Another approach is to look at the proportion of days per month in which the minimum temperature is equal to or greater than 16oC (a more or less arbitrary high value).    On average for December this is 3% (ie one day per year).  For 2016 there were 5 (16%) such days, the highest recorded and in percentage terms higher than January - the month with the highest average % at 12.5%.

Looking at heat waves (ie periods of 3+ days of maxima >30oC and minima >10oC) we were again about on average, but well below 2015.
There is a small element of technicality in this as one night had a minimum of 9.9oC and had that been 0.1oC higher the value for December would have been 12 rather than 9!


The first chart shows clearly that the 15:00 humidity bounced up as the rain events arrived. Apart from those times the first half of the month was quite dry while the second half showed a rising trend, but not dramatically different to my "fair" value of 40%rH
Taking a longer term view the month was slightly more humid than usual, but a lot more so than last year.


The daily maximum gusts generate a chart that, as usual, resembles a poorly sharpened saw blade.
 Compared with past Decembers the average gust is right on normal.

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