Thursday, 1 March 2018

Weather Report February

Here is the Gazette-format summary.
 I wondered what the fire danger was like after the weekend rain (and cool weather on 26th and 27th.  The answer was very green everywhere!
I then wondered how frequently the entire State was Low/Moderate fire danger in February, but given the RFS can't put the date in a graphic, I doubt if they could answer that question!


I have done an ad-hoc report on the rainy weekend.  The conclusions from that are that it was a very wet period in an otherwise dry month, but there didn't seem to any trend in the variability of rainfall in Februarys.

This month we ended with 53.4mm of rain which was a) better than last year but b) still a long way below average.
Applying a simple prorata extrapolation to the rainfall to date gives a total of 433mm expected for the year.  However using extrapolation of a trendline (dodgy with only 2 observations) gives a much more reasonable, but still low, expectation of ~615mm.
It is very interesting that the two trend lines in that graph are almost parallel with the major difference in the equations being the 2.4mm difference in the origin.


At various points it looked as though this month was going to be a scorcher but overall the temperatures were not too bad,  A couple of relatively cool changes later in the month are clearly shown by dips in the Maximum line (and to a lesser extent in the Minimum line).
The average temperature for the month was lower than last year and almost exactly on the average of averages.  Again supporting the statement that temperatures were not too bad.

Maximum Temperatures

The average maximum temperature for the month was, as with January, below last year and almost on the average .
 Looking at the period since 2010 there is a fair bit of fluctuation in the average maximum temperatures for February.
 My final look at high temperatures is the number of heat wave days.  I define a heat wave as a period of 3 or more consecutive days with maximum temperatures above 30oC and minimum temperatures above 10oC.  This year we had only one heat wave, lasting 7 days.
 There were another 5 days over 30oC but in isolated 1 or 2 day bursts.  It is interesting that if the criterion was dropped to 'over 29oC' we would still have only had one heat wave - but it would have lasted for 16 days!

Minimum Temperatures

The average minimum temperature for February this year was considerably lower than for  January this year and a little lower than February last year.  However it continues the experience of the last 14 months of being above the long term average.
 Again looking at the period since 2010 the pattern is a little unusual as the first 2 years are oddly high compared to the fairly constant averages between ~11.5oC and 12.5oC.


The standard graphic shows that average humidity at 1500Hrs for the month was a  fair amount below average.  
Looking at daily readings, and taking 40% as a reasonable average, 15 of 28 days were below that value.  The lowest value - on 15 February - was 14% (the third lowest recorded since November 2013) and the 16% recorded - on the 18th - was the 4th lowest.

I have also included readings for 0900Hrs in the chart below as I noticed as the month unfolded that some of those values were very low.

The values for 10 February are particularly interesting showing a very dry morning and a very damp - raining - afternoon.

The next chart is possibly so complicated as to become meaningless, but I found it interesting as it compares daily values for February 2018 with the average values for that day over Februarys since 2013.
I have boxed the very dry 1500 reading early in the month while the ellipses mark very dry afternoon readings.


As I usually confess my WS is poorly placed to record wind so I only do a minimalist analysis of that attribute of the weather.  The first chart shows that it was a pretty drafty month in comparison to other Februarys.
The next chart shows the maximum gust recorded each day.  My recollection is that the day with the highest gusts -14th was one of several during the month where storm cells appeared but the rain split around us! The second peak on the 24th was the lead-up to the very rainy period.

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