Weather Report February 2020

My one line takeaway for the month is quite damp with moderate temperatures.

The dampness manifests itself in both rain and morning humidity being above average.  Winds were quite modest in run, but rather surprisingly focused on the SE quadrant rather than the NW as was the case for most earlier months.

Rain

We finally got some!  The total fall for the month was 110.8 mm which is the 8th heaviest fall recorded for a February. That is of course comparing with BoM records and unusually this month was wetter at home than the BoM sites at Mallacoota (84.8 mm) and Gabo Is (78.2 mm).  The fall was well above well above last year and the median.

This means that my pro-rata extrapolation for the year in total is quite impressive currently standing at 1105 mm.

Temperatures

Overall the anomaly (the difference between the current average and the long term average for February - both calculated using BoM data) was 0.4^oC.  This is largely a balance between warm overnight temperatures (21 of 29 days had a warmer than average minimum) and cool daytime temperatures (19 days with a minimum below average).

Here are the daily maxima and minima.

Maximum temperatures

My Weather Station recorded an average maximum temperature of 25.1^oC a little above last year and the long term (mainly BoM) average.

The BoM average for the month was 23.2^oC: a little below average, as would be expected following my comments in the preamble to this section.  This is not unusual as the maximum temperature at the coastal BoM site is often moderated by a sea breeze kicking in around noon.

In Summer I look for heat waves - 3+ consecutive significantly above normal maxima.  Taking "significantly above normal" to mean greater than average maximum + 1 standard deviation, gives a threshold temperature of 28^oC.  In 2020 we did not record one such period: the 3 days from 23-25 February came close, with maxima of 30.6, 27.9 and 33.2, but the middle temperature prevented a cigar being awarded.

Minimum temperatures

The average minimum recorded at my Weather Station was 17.2^oC just above the highest average minimum of 17.15 recorded by BoM (in 2010).  This month the BoM average was 16.8^oC (although readings were not available for a couple of days, probably with warm minima based on readings at Gabo).  This is the equal second highest minimum recorded for February.

In view of the warmth of the minimum for 2020 I thought it worthwhile checking time series.  While a trend line in the time series (data available for February since 1994) shows a rising slope the value of r² makes it clear the 'trend' is not significant.

A much longer time series - reliable since 2010 - is available for Gabo Island.  That shows that the series varies considerably from year to year, but within a quite narrow band and with no significant trend.

Humidity

On a daily basis the month seemed to offer quite humid weather (duhhh - check the rainfall).

Looking at the monthly averages the morning value was well above the average and the value for last year.

 The afternoon reading was well above last years value but not much above average.

Wind

Although there were a few draughty days there was relatively calm.  In the next chart I have included a series titled "avg adjusted": this includes data from the BoM site adjusted by the ratio of the annual average wind runs at my weather station and the BoM site.  (My site is 45% of the BoM site.)  Somewhat rubbery, but gets values to the same scale.  On that basis February 2020 was less windy than the previous year (both measured at my site) and the adjusted average.

 As shown by the daily wind runs the winds were quite temperate other than the 23^rd when the hourly runs were close to 20km from midnight to 1400hrs. 

Checking wind direction at my site the modal direction was ESE.  This is similar to the situation in January but I feel somewhat different to previous months where the biggest direction was close to NW.  I am having difficulty in showing that.

Weather Report January 2020

This has been a very difficult report to compile both from the view of having data to access and refraining from making excessive commentary on the data I have available.

A particular problem arose with the BoM site for Mallacoota not reporting for a total of 10 days, making it almost impossible to use that data for historical comparisons.  Fortunately my personal site kept running even though the console would have been running on batteries for 14 days.  Where at times my records appeared to conflict with those from the BoM sites at the airport and/or Gabo Island they proved very consistent with those from a private site in town which is linked to internet (as long as power is available!) and provides a better reflection of conditions in town than the airport site...

Clearly the month was very dry, with a storm on 20 January the only major fall.  Most of the month was relatively cool due to the smoke coverage keeping the sun off.  Late in the month this had the somewhat contrary "blanket effect" of holding the heat in giving very high minima.  Humidity was abut normal.  Wind strength was as expected although it was unusual to find a high proportion of the wind coming from ESE rather than nnw.

Rainfall

Pathetic.  A little more than last year, but still well below average.  The concentration of the fal into the storm on the 20th is clear in this chart.

The number of days with falls above 0.2mm was, at 9 days, surprisingly a little above average for the month.  (The average was taken from BoM  data since 1974 and excludes the period 1979 - 1984 inclusive where it was common to find the reading spanning several days.)

Temperatures

My usual overall measure of temperatures is the anomaly taken as the difference between the average for the reference period and the long term average.  That is made very difficult for this year as the BoM site was out of action for 10 days.  I thought of using Gabo Island as a proxy but that also failed to report for 5 days.  My conclusion to this was to calculate  the anomaly using the days for which the sites had a 2020 value available. 

 As well as calculating the anomaly I have plotted the recorded value for 2020 and the average for the day.  As Gabo has more days available I have shown that first.  Note that I truncated the vertical scale to show more clearly the comparison between the two series and not out of an IPA/Murdochian shokanorror desire to panic people.

Looking at the charts it is not surprising to find that the anomaly for Gabo (+1.3^oC) is greater than for Mallacoota (+0.2^oC).   I believe this can be attributed to the skies at Gabo being less opaquely smothered in smoke.  For an assessment of comparison with long-term trends (who said "Climate Change"?) I believe the value for Gabo is a more useful indicator than that for Mallacoota.

A second approach to overall temperatures is to look at the daily extremes through the month.  These data are from my Weather Station.

I was quite surprised at the fluctuations.

Maximum temperatures

The highest temperature recorded at my WS in the month (38.0^oC) was on the 31st while the BoM site got to 34.9 on the same day. I plotted the maxima at my WS against those available from BoM:

 As expected my WS readings are higher than the BoM data (exaggerated by the truncated scale) due to the sea breeze kicking in in the afternoon.  However I believe that the long term average data for the BoM site provides a useful background for comparison on current values and in the chart below the 2020 value is from my WS while the other 2 values are BoM.  (From March onwards the 2019 value will also be from my WS.)

Of course, for refuting the views of climate change denialists (if anyone still espouses such views after this Summer) the argument will always be mounted using only the more consistent information from BoM.

The other interesting aspect of maximum temperatures in Summer is that of heat-waves.  The BoM defines a Heat Wave as 3 consecutive days of significantly above average maximum temperatures.  Taking this to mean the long term average maximum plus 1 standard deviation gives the lower limit for a heat wave in January of 25.1^oC.  My indicator statistics is number of Heat Wave Days HWD in a month - that is counting the number of days that contribute to heat waves in the month.  For 2020 there were 8 such days (including the 30th and 31st (both over 25.1^oC as was the 1st of February)!

I shall do an analysis of the cut off temperatures for other months and thus a time series of HWDs.

Minimum temperatures

The month concluded with an extremely warm minimum on the 31st (BoM 22.9^oC, WS 23.1^oC).  The BoM reading was the 4th highest on record (stealing February's thunder: the value (24.0^oC) on 1st February equalled the all time high minmum for Mallacoota).

The BoM and WS values were very close.

 This year's average minimum was a bit above average but less so than 2019.

Humidity

The daily numbers especially for 1500 hrs, vary greatly though the month.  RH of close to 40% is very low for a coastal site.

 The morning value was higher than 2019 and the historic BoM average.

 The afternoon value was a touch under average and considerably below the value for 2019.

Wind

The average daily run was 137 km which is reasonably high when compared with other values for my WS.  The little data on wind published (at no cost) by BoM suggests it is of a broadly correct order of magnitude.

The wind rose is interesting in showing a high proportion of wind coming from the ESE, rather than the more usual NNW - N section of the rose.

An initial review suggests the wind mainly came from this direction for the period 17th to 29th.  The very hot weather of the 30th to 31st reflected a return to N winds.

Weather Report December 2019

In summary hot and dry.  What follows is nearly all based on BoM data as I haven't had access to my WS since 30 December, when we left for Canberra.

Rainfall

By the time we left my WS had recorded 3.4 mm for the month, which was the total.  While this is a little less than the BoM total (11.2 mm the second lowest for the month since 1975) the reading for Gabo Island was 6.6 mm and I overheard someone in town saying they had only recorded 1.8 mm for the month.  Using BoM data for every month here is the sorry picture for the year.

Looking at annual totals the BoM result for 2019 (595.2 mm) is the lowest on record since 1975.  The previous low (in 1980) was 675 mm.  Taking BoM data for January (before we arrived) my estimate for Ango[hora Dr was 536 mm. 

Temperatures

A first overall comment is that the BoM have not given a maximum temperature for 30 December.  I initially thought that was because their station recorded - in the hourly records  -  a maximum of 49.1^oC at 0800 hrs as the fire front came through. However the fire came through on the 31st - but as it was before 0900 it got "counted" for the 30th: complete rubbish. For the 30th I have used an estimated maximum for that day of  26.9^oC which is the value at 0835 on the 31st.  This is possibly an understatement but I can no longer access the hourly records for the 30th. For most of the 31st the site offered 16 - 19^oC, probably due to the heavy smoke cover and the SW wind.

.The overall view of the temperature is given by the anomaly, which is the difference between the current and long term mean temperatures.  For December 2019 that ended up at +2.41^oC.  The month began cool but then steadily heated up.

A second overall approach is to look at the daily extremes.

Maximum temperatures

Overall the average daily maximum was well above both long term average and 2018.

The maximum temperature was above average on 25 of 31 days!

Minimum temperatures

Surprisingly the mean minimum was below average, I think reflecting the cool mornings from the 1st to the 3rd.

The minimum was above average - sometimes less than 1^oC - on 20 days.

Humidity

Referring only to the BoM data the most surprising fact is how closely the 2 series mirror each other.

 The average for 0900 was 61.4% well down on last year and the average

Wind

The BoM data for Mallacoota includes a maximum gust of 100 kph on 31 December.  I suspect that is fire-related anomaly.  I can't really work out which of the BoM are reliable or what they mean in the absence of my WS data so will say no more.

Weather report November 2019

Overview

I'm afraid there isn't a great deal of detail in this as a few issues have distracted me in early December.  I hope to get  to a series of thematic posts in the next week or so.

Overall a mild month with slightly below median rainfall and strong winds (an evil plot to stop us going out in our kayaks)..

Weather characteristics

Rainfall

We recorded 52.2mm for the month as a whole which at 83.5% of median would not be too bad were it not for:

• only recording 2 months so far this year with above median rainfall; and
• somewhat over half that fall occurring on a single day early in the month (and the only other day with >5mm being the next day).

In terms of history we were, as noted above, below median and very much below last year,

In terms of the possible annual fall, assuming a median fall in December the BoM site was  up (? down might be better) to 656 mm.  This would be either the lowest or second lowest fall recorded since 1975.

Temperature

The best overall measure of temperature is the anomaly calculated as the difference between the mean monthly temperature and the long term average.  BoM data was used entirely for these calculations.  In November that ended the month at -0.1^oC.  The chart shows that the first two days were were hot, but the remainder of the month was quite mild.

The commonest situation (12 of 30 days) was for both minimum and maximum to be below average.  The other three cases (both min and max > average, one above the other below) were even at 6 days each. 

My second overall measure is a presentation of the daily extremes

The highest maximum was 38.8^oC - below the BoM reading which got to 40.7^oC on the 21^st.

Maximum Temperature

The mean maximum temperature was well above the long term average and last year.

Minimum temperature

In contrast to the maximum this was below both the long term value and last year.

Humidity

Both readings for humidity were well below last years's wet November, the  value for 1500 hrs noticeably so

Wind

The month seemed quite windy which is supported by the data.  The longest wind run was 444 km which is the third longest this year, and the strongest gust  64.4 kph (also 3rd highest this yearon the 21st (as the change came through after the hot day).

There is little to compare with but the overall change from previous months looks similar to a long term average.

In terms of wind direction we moved to a Summer pattern with more winds from close to South rather the NW to N.  I shall look at this more closely in the near future.

October 2019 Weather Report

Overall the month was about on average for mean temperature and 15% below median rainfall.  Humidity was higher in the morning but lower in the afternoons.  It was less windy than past data would suggest and the wind came more from the East than has been the case in past months.

Rain

I recorded 50.2 mm for the month (BoM: Mallacoota 52 mm; Gabo Island 40.4). As noted above this is below the median for October but well above October 2018.

Longer term rainfall analysis

Using a pro-rata method to estimate the possible annual rainfall given falls to the end of the month comes up with a result of 578 mm - a slight improvement on the situation at the start of the month.  

Someone recently mention a 3 year drought so I have examined the situation using rolling averages for 12, 24 and 36 months.  That is summarised in the following chart.

This shows the local peak of the 36 month series as October 2016 - exactly 3 years ago!  The 12 month series shows a period of decline starting in April 2015. 

The longest period of decline in the 12 month series is from 1989 to 1995 - close to 6 years!  I hope we don't break that record. The 12 months from June 1994 to May 1995 average 45 mm per month: other months in 1994 - 95 have more rain bring the calendar year averages up to more healthy levels.

Temperatures

My overall summary of the temperature is the difference between the mean temperature for the month and its long term equivalent (in both cases using BoM data for Mallacoota).  For October that ended up at +0.04^oC - effectively at the average.  The development of that anomaly through the month shows an early period of warmth, cool through most of the month and a warm sting in the tail.

Looking at the relationship of the daily extremes to the average values for that data shows the most frequent situation was for both measures to be below average.

Another way of showing the temperatures is the daily temperatures recorded on my weather station on Angophora Drive.

 On looking at that chart I was struck by the range of temperatures on some days and the day to day  variation in the range.  I charted that together with average range for the date and the values for 2018.

Eyeballing that graph it appears that the ranges seen had some unusually high values and the level of variability was higher than most years.

Maximum temperatures

The highest maximum recorded was 34.9^oC on the 31^st.  The monthly average maximum was 19.9^oC.  This is above average, but a little cooler last year.

The series since 1993 does not show a significant linear trend.

Minimum temperatures

The lowest minimum for the moth was 5.4^oC on the 13^th.  The monthly average minimum was 9.8^oC..  This is slightly below average and last year.

Again no significant linear trend in the series.

Humidity

The morning and afternoon values are generally quite similar with few morning fogs and some quite low values towards the end of the month.

The morning value is higher than last year and the history shown by BoM while the opposite is the case for the afternoon value.

Wind

Although it appeared to be quite a windy month records from my WS do not confirm that.  (The BoM has several days missing for their only indicator (maximum gust) for Mallacoota so is even less helpful than usual for wind!)  In addition the windrun was lower for October than for September, which goes against the few snippets of past data available from BoM.

As there was a disjoint between my expectation and the observations I looked at two measures of "windiness" and the pattern is broadly similar (correlation coefficient 0.64) so conclude that my WS is not failing.

Possibly the most surprising observation for the month is a relatively high (22%) of hourly wind records coming from the ESE.  

Looking at previous WS records it seems that this increase in winds from ESE is balanced by a decrease in those from the NNW and N directions.  As the WS has not changed position (nor has the wind vane been interfered with) I can only assume this is a seasonal shift.