December 2015 weather report

An El Nino event was promised for the end of the year and this was not an idle threat.  Dry, hot and windy is my normative view of the month, so it will be interesting to see what the data says.  Cutting to the chase, I think my view is confirmed, although it turns out to not have been very windy for much of the month.


The usual chart really says it all.
This was the lowest (by 2mm) rainfall we have recorded in 9 years.  107mm down on last year and 64mm below the 8 year average.  Only 2 days above 5mm of rain.  That counts as a dry month.


The month seemed to be a series of cycles of warming followed by a brief drop back to more comfortable levels.  We recorded temperatures over 30oC on 13 days and dropped below 10o on 17.  The low temperature of 3.3o on 12 December was a major surprise.

This basic theme of hot days and cool nights is carried through to the averages.  With the maximum being 2 degrees above the (3 year) average .....
... and the minimum being slightly below average.
Looking slightly more closely at the minimums, it seems that 2014 may be the outlier with a warm value, due to the cloud of a wet months holding the warmth in.


The basic pattern is of low humidity with occasional spikes on the rainy days.
Following an informal comment by a hydrologist that 40%rH is a reasonable value, I regard anything below 20% as a low value.  (To give a context, on the day of the 2003 bushfires, the reading in Canberra was apparently 4%.)  In December 2015 we recorded 5 days with rH values below 20% which appears to be about normal.

Comparing with the average the same story appears as with minimum temperatures: a lower than average value as December 2014 was pretty damp.


The default situation for wind this month seems to have been for a daily maximum gust between 15 and 20 kph.
 The obvious exceptions are the period from 7 to 10 December and to a lesser extent the 16th to 18th.  The first of these periods resulted in no rain, while the second period followed a few showers on the 16th.  The most rain occurred on the 26th which was relatively calm.

In terms of average gust the month was windier than most months this year but less windy than the average December.  Possibly the most interesting aspect of this chart is the low value of R2 for the series of 2015 readings: obviously wind has been all over the place this month.


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