Thursday, 2 June 2016

Weather Report May 2016

Material from Stony Creek Gazette advice

Site now based at Whiskers Creek Rd. For details of history see this post 

Temperatures
(Jan 1993 to date)

Current year

Max
Min
Average
May
23.2
 -4.7
 9.2
Past years
Max
Date
Min
Date
May
27
12 May 2007
-8
 07-May-97
All Months
45
 24 Jan 2001
-10
 02 Aug 1997
Rainfall
(May 1984 to date)


Current year
Past years
Total
Average
Max
Min
May
47.2
38
155
1
Annual total
556 (est)
659
1005
410

Detailed comments

The following is my more usual more detailed coverage of the last month both in its own right and looking at it relative to the history.  For temperatures and rainfall a much longer time series is now available.

As there may be a number of new readers of the weather report this month I will explain a bit more about the interpretation of some of the whackier charts etc.  I hope that doesn't annoy any of you who have read previous examples.

Rainfall

The regular reader of these posts may notice that the averages (blue columns) have changed a bit.  That is because I am now using 32 years of data rather than 10. 

After a very dry April, May was a little above average with 47.2mm, with above 0.2mm recorded on 5 days (I use "above 0.2mm" since a decent mist is recorded as 0.2mm)!    This was not so much so as to cause the Creek to run above light flow levels (but at least it did run for much of the month).

Temperatures

This graph contains a fair heap of information about temperatures over the past month.  The top of the green lines is the daily maximum and the bottom the daily minimum.  Thus the length of the bar indicates the daily range in temperatures.  The boxes relate the temperatures at 00:30 and 23:30and thus indicate the change in temperature over the day.  A red box shows that the last temperature was higher than the first and a blue box is the opposite.  The length of the box shows the size of the difference.

Overall the temperatures oscillate through the month with - as would be expected - an overall downward trend.  The first 'serious frosts. -4.5oC and -4.7oC came right at the end of the month.

Having raised the matter of frosts I have looked at the number of days each month  on which frosts have been recorded.  The next graph defines a frost as a temperature of +2oC (as that temperature at an official screen height is equivalent to a temperature of 0oC at ground level).  My Dad - in the UK - used to call these ground frosts and they weren't 'serious'.
When it is cold enough for the air at screen height to be below 0oC it is an air frost and a matter of serious concern to a commercial tomato grower such as Dad.
As expected the incidence of air frosts is much less than ground frosts. By both measures there have below average numbers of frosts so far this year (although there have been more air frosts than 2015).

Going back to overall temperatures the average maximum temperature for the last month was pretty much in agreement with the average and and the vaue for 2015

The average minimum is a bit higher than both the long term average and (somewhat surprisingly in view of the frost comparison) 2015.  I suspect this is due to a rather warm period around the 8th/9th.

Humidity

As usual I concern myself with the relative humidity at 3pm (as do BoM).  
Taking a rule of thumb that a reading of 40% is 'normal', this month is well endowed with normal.  The only exceptions are a couple of the rainy periods, which are well above 'normal'.  As is usual moving into cooler weather, there are no periods of very low humidity..
Looking at the longer term average (and here we are back to my 10 year series) the month was very consistent with 2015 and the long term average.

Wind

The month felt a bit windy and so the graphs show.  The maximum gust was above 30kph on 7days.
 Looking at the longer term measures this was by far the windiest month I have recorded.  I am always a bit suspicious of wind readings since my anemometer is mounted too low (and occasionally gets mucked up by spider webs) but I think it is safe to conclude that May 2016 was a very windy month!

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