Posts Tagged ‘weather’

Unprecedented South Australian Weather!

January 22, 2017

(and it has been like that for 178 years!)

There were more blackouts in South Australia a couple of days ago following a wild storm.  In a report in the Adelaide Advertiser, SA Power Networks spokesperson Paul Roberts is quoted:

“This is just another example of the unprecedented weather in the last six months,” Mr Roberts said, referring to bouts of wild weather that have hit power supplies hard this summer and the preceding spring.

21mm of rain was measured at the Kent Town gauge.

Just how “unprecedented” is Adelaide’s weather over the past few months?  I couldn’t find any records for the number of severe storms, so for a proxy I have made do with rainfall data from West Terrace and Kent Town in Adelaide.  The overlap period has very similar rainfall recordings so I joined the two series to give a record starting on 1 January 1839.  That’s 178 years of data.

When thinking about “unprecedented”, we need to check amount, intensity, and frequency.

Firstly, a few plots to give some context.  How unprecedented was Thursday’s storm?

Fig. 1: Rainfall for the first 21 days of January compared with Days 1 – 21 of every year

adelaide-rain-21-jan

Note Thursday’s rainfall had less rain than four previous occasions on this day alone, and 20 or so in previous Januarys.

Fig. 2: Rainfall for each day of 2016 compared with each day of every year:

adelaide-rain-2016

Note the December storm had extreme rain (for Adelaide) but not a record.

Amount and intensity has been higher in many previous years.  141.5mm was recorded on 7 February 1925.

Fig. 3: 7 day average rainfall over the years:

adelaide-rain-2016-7d-avg

The topmost dot shows the maximum 7 day average for each year.  2016 got to 13.4mm on 4 October- multiply by 7 to get the weekly total rain.  Note there were many wet and dry periods all through the record.

21mm of rain fell in a severe storm on Thursday, so I arbitrarily chose 20mm as my criterion for heavy rainfall in one day as a probable indicator of stormy weather.  I am the first to admit that 20mm might fall steadily all day and not be at all associated with wild winds, and wild winds can occur without any rain, but bear with me.

Fig. 4: Rain over 20mm throughout the year:

adelaide-rain-2016-above-20

There seems to be no increase in amount or intensity of rain at any time of the year.

Fig. 5: Frequency:

adelaide-rain-2016-cnt-above-20

Note 2016 had 7 days with above 20mm in 24 hours.  That’s the most since… 2000, when there were 8 days- and many previous years had 7 or 8 days, and 1889 had 9.  So no increase in frequency.

However, Mr Roberts was referring to the last six months, spring and summer.  So let’s look at rain events over 20mm from July to December, firstly amounts recorded:

Fig. 6: July to December Rain over 20mm:

adelaide-rain-above-20-last-6m

Nothing unusual about 2016.

Fig. 7:  Frequency of heavy rain July – December:

adelaide-rain-2016-cnt-above-20-last-6m

1973, 1978, and 1992 had the same or more days with over 20mm.

I now restrict the count to spring and summer only:

Fig. 8:  Spring and Summer frequency:

adelaide-rain-2016-cnt-above-20-last-4m

Not unprecedented: 1992 had one more.  Add in last Thursday’s event to make them equal.

Conclusion

Adelaide has a long climate record, showing daily rainfall has varied greatly over the years.  There is no recent increase in amount, intensity, or frequency for the whole year, or for the last six months or four months.  Spring and summer rainfall in 2016 was not unprecedented, and to the extent that spring and summer falls over 20mm are a proxy for storms, there is no evidence for an increase in wild weather.  This is normal.  Get used to it, Mr Roberts, and make sure the electricity network can cope.

 

Putting Temperature in Context: Pt 2

December 14, 2016

To show how handy my Excel worksheet is, here’s one I did in the last 15 minutes.

Apparently Sydney has had its warmest December minimum on record at 27.1 C.  The record before that was Christmas Day, 1868 at 26.3C.

The following seven plots show this in context.

Fig. 1:  The annual range in Sydney’s minima:

whole-yr-sydney-min

Extremes in minima can occur any time between October and March.

Fig. 2:  The first 2 weeks of December

14d-sydney-min

Plainly, a new record was set this morning, but apart from Day 340 the other days are within the normal range.

Fig. 3:  7 day mean of Tmin in this period

7d-avg-sydney-min

Extreme, but a number of previous years had warmer averages.

Fig. 4:  Consecutive days above 20C Tmin.

days-over-20-sydney

But there have been longer periods of warm minima in the past.

Now let’s look at the same metric, but for all of December.

Fig. 5:  All Decembers (including leap years).

december-sydney-min

A record for December, with 1868 in second place.

Fig. 6:  7 day mean of Tmin for Decembers

7d-avg-sydney-min-december

Seven day periods of warm nights are not new.  The horizontal black line shows the average to this morning (20.6C) is matched or exceeded by a dozen other Decembers.  (Of course this December isn’t half way through yet.)  Also note what appears to be a step change about 1970.

Fig. 7:  Consecutive days above 20C Tmin in December.

days-over-20-sydney-december

I doubt if 15 December will be as warm as today, but could still be over 20C.

This is weather, not global warming.

 

When Tmax and Tmin Are Poor at Describing Weather

October 25, 2016

Last Sunday was a miserable day in Rockhampton- overcast with drizzling rain and cold all day.  Mean maximum for October is 29.7 degrees, so the maximum reported by the Bureau of 20.4 was 9.5 degrees below average, as expected.  However, that does not tell you anything like the whole story.

Here is the temperature graph from the Bureau for the period midday Saturday to midday Tuesday.  The solid horizontal line shows the duration of Sunday 23rd, and the thin black vertical lines show 9.00 a.m., which is the time when the daily minimum and the previous day’s maximum are recorded.   Temperatures at recording times are circled.

rocky-temp-23-oct

On fine, clear days, minima usually occur around sunrise and maxima in the early afternoon: you can see this on the 22nd, 24th, and (almost) on the 25th.  Sunday 23rd was wet.  As you can see the temperature was falling fairly steadily from Saturday afternoon until Monday morning.   The maximum for Sunday was 22.7 at midnight, and the coldest temperature on Sunday was 14.3 from 7.30 p.m. to 9.00 p.m. on Sunday night- not the 17.6 at 9.00 a.m.   The official maximum for Sunday of 20.4 degrees was actually the temperature at 9.00 a.m. on Monday!

So what was the Diurnal Temperature Range?  Was 20.6 (or 22.7) a good representation of how high the temperature “rose”?  The temperature in the early afternoon varied between 15 and 16.4, and this was about 14 degrees below normal for this time of the year (and two to three degrees below the official lowest maximum of 18.1 on 10th October 1982).

Which is one reason I don’t take a lot of notice of claims of hottest or coldest extremes.

Was 2013 the Hottest Year on Record? Update!

January 6, 2014

Update:  Warwick Hughes has reminded me of his post on 5 December at http://www.warwickhughes.com/blog/?p=2496 where he shows a distinct drift in UAH data compared with RSS, and in later posts he confirms this in southern Africa and the USA.  Warwick says:

"I have checked UAH against CRUT4 and GHCN CAMS for all Australia and it
looks like there was a drift in UAH 2005-2006.

Until UAH resolves the issue, I think their ranking of Australian hot
years is not worth repeating."

That may help explain the large divergence in recent years.  

I will leave this post as is, with the caveat that it is based on available UAH and Acorn data.

Yes.

On Friday, 2 January, the BOM released its Climate Statement claiming 2013 as the hottest year on record.

The UAH dataset for lower troposphere temperatures has also been just released.

I have compared BOM monthly data with UAH by converting the BOM anomalies to the same reference period as UAH (1981-2010).

Here is the result:  UAH vs BOM 1978-2013 (12 month running means)uah v bom

It is plain to see that in the satellite era, Australian surface temperatures (as calculated by the BOM) reached a record last year.

For the 12 month periods to December, UAH agrees that 2013 was the hottest, just ahead of 1998 and 2009.

According to UAH, the 12 months period to October 2013 was just edged out by the 12 months to June 2010.

So, the BOM is right in saying 2013 was the hottest on their 104 year (and very much adjusted) record.

While the two datasets match reasonably well in most years, especially 1996-1999, they diverge markedly in recent extreme years.  It appears that the BOM area averaging algorithm accentuates extremes, probably because of the scarcity of observing sites in the remote inland, where warming and cooling are much greater.  Alice Springs, for example, being hundreds of kilometres from the nearest neighbouring site, contributes 7 – 10% of the national warming signal.

As well, the satellites’ remote sensors do not necessarily match the atmospheric conditions at ground level, depending on different seasonal conditions.  However, to quote Dr John Christy, “the temperature of the lower troposphere (TLT) more accurately represents what the bulk atmosphere is doing – which is the quantity that is most directly related to greenhouse gas impacts.”

So- if you are interested in the weather, how hot it is locally, consult the BOM- the old Weather Bureau.  If you are interested in whether the climate is changing due to greenhouses gases, consult the satellite data.

And yes, the weather has been hot (and still is where I live).

No Warming in North Australia for 31 Years

December 23, 2013

I’m nearly a year late with this, but I’ve only just noticed.

According to the Bureau of Meteorology’s official temperature records, for all of the Northern Australian region- the half of the continent north of 26 degrees South- the minimum temperatures are steadfastly refusing to rise.  From 1982 to 2012, the linear trendline for minima is on the decreasing side of dead flat.

Acorn tmin Nth Oz 82-12

This is longer than the 3o years regarded as the minimum period for analysing climate trends, and in spite of the massive increase in amount of CO2 emissions.  Note that 1982 and 2011-2012 were almost equally cooler than normal.

Remember  that one of the fingerprints of greenhouse warming is that minima should be increasing more than maxima.

Here is the 365 day running mean of daily minima anomalies of all Acorn sites in Northern Australia (more about this next year) up to early December this year:

tmin nth aust 1910-13a

Rather than a smoothly rising trend, the record is characterised by 10 to 15 year rapid rises and falls, responding to events in the Pacific and Indian Oceans.

This is a diagram of Australia’s climate regions:summer1213  regions

After New Year I will post about minima for other regions and Australia as a whole.

Merry Christmas to all.

Weather predictions: December

December 1, 2013

At the start of November, I said:

“November
5 to 10 unstable; 13 to 21 unstable with several events; 26-27-28-29-30 unstable.”

All correct, 1 miss.  Instability with some very wild storms marked much of November especially in the South-East of the state.

Now I suppose anyone could have predicted storms for November.  But remember, back in August I had said:

“November

5-6-7, 9-10, 13-14-15, 17-18-19-20, 27-28-29.”

Here’s a chart showing August predictions in light green and early November predictions in dark green.octdec13resultsnov

5 right, I miss.  I should have stuck with my original predictions!

So the method is holding.

Predictions for December to 31 March remain the same as I predicted last month.  As well, I expect weather events around these dates in April and May (+/- 1 day):

2,4,7,11,15,20,23,25, May 1, 8,11.

April should have unstable weather, and I would not be surprised if we get significant rain.

 

Weather Predictions November – March

November 3, 2013

At the start of October, I made the following predictions:

October
Sep 30- 1-2, 8-9-10, 14-15-16, 20-21-22-23, 25?, 28-29-30-31-Nov 1 (possibly 2 events).

Changes were detected on:- 2-3, 8-9, 13-14, 17-18, 22-23- 24, 28- 29-30-31 (the”possibly 2 events” was true indeed with a series of storm fronts that persisted.)Oct 13 results & pred

Dark red is Tmin, pink is Tmax, black is inverted pressure, blue is rain, green is the 160 day lagged Tmin, yellow is 40 day lagged pressure.  I may try 40 day lagged temperature in future.   November and December predictions are shown as red ovals.  So there were 5 correct predictions, 1 wrong, and 1 miss (although the wrong event would have been a “correct” if it had been a day earlier).  Not bad for 160 days out, I console myself.  I also suspect there has been a slight acceleration of weather systems, so perhaps I should be looking at events around 158 days ahead instead of 160.  No matter for now but I will keep an eye on it.

Predictions for November and December (slightly adjusted from last month):

November
5 to 10 unstable; 13 to 21 unstable with several events; 26-27-28-29-30 unstable.
December
2 to 10 unstable; 12-13-14; 16-17-18-19; 22-23-24; 26 to 31 unstable.

 January to March:

Here is the graph I use for predicting weather changes, which shows 2nd derivative, or acceleration/deceleration, of minimum temperature.

jan-mar 2014 predictions

Think of a cool change moving through from the west.  A large temperature differential, or a fast moving change, both have the same effect.  When the green line goes below zero, the temperature has decelerated, and a change (or unsettled weather) occurs in the time period indicated.  Several rapid oscillations appear to relate to unsettled weather.  My only problem is I am averaging over a very wide region, and the time lag may be changing.

There is always something to learn.

October- December Predictions

October 2, 2013

At the start of last month, I said:

“A vigorous change came through the Capricornia district today, and further events are expected on:  4, 7, 9-10, 13, 16-17-18, 23-24-25, and 30- October 2.”

Results in September have not been as successful.  Changes occurred on September 2, 10, 13-14, 17, 25, 27, and storms brought rain to some places in the last two days.

6 right, 3 wrong, and 1 miss (which in hindsight I should have seen.)

75% right, 25% wrong, and a miss- not good.

For the rest of the year, I am predicting weather events (storms, heat followed by cool changes, dry fronts moving through) at the following times:

October
Sep 30- 1-2, 8-9-10, 14-15-16, 20-21-22-23, 25?, 28-29-30-31-Nov 1 (possibly 2 events).
November
4; 6-7; 9-10; 13-14-15; 18-19-20-21; 27-28-29.
December
5-6-7; 8-9-10; 12-13-14; 17-18-19; 22-23-24; 26-27-28.

For January-March 2014:  If I get within a day or two of these I’ll be happy.

January:

5, 9?, 14, 20-26 unsettled.

February:

6, 10, 16?, 21-24, 27?.

March:

4-9 (unsettled).

Concerning how hot September was:

Yes, it was hot.  Many daily and monthly records were broken.

For the 10 sites I monitor, all but Rockhampton, Maryborough, and Amberley broke daily and monthly records.  Rockhampton equalled the monthly record but had no chance of breaking the 37.9 (corrected to 37.4) daily record mentioned in the 1953 Commonwealth Year Book, p.44.  (And Brisbane was not even close to 38.3 set in 1943.)  Inland was very hot.

The 365 day mean of maxima has been above average all year.

Australia’s warmest 12-month period on record- NOT

September 11, 2013

Ken Stewart

September 2013

Australia’s Bureau of Meteorology (BOM) was quick off the mark earlier this month when it proclaimed:

Australia’s warmest 12-month period on record

September 2012 to August 2013: the last 12 months

The past 12 months have been the warmest on record for Australia. The average temperature across Australia for the period 1 September 2012 to 31 August 2013 was 22.92 °C. This is 1.11 °C above the 1961–1990 average, surpassing the previous record of +1.08 °C that occurred between February 2005 and January 2006.”

The satellite data for the mid-troposphere for Australia- Land has just been released by the University of Alabama- Huntsville (UAH).  Unfortunately analysis of this data shows that the mean temperature for the 12 months to August 2013 was +0.668 Celsius, which makes this period the sixth warmest of the satellite era (since December 1978).

Image

That’s 0.087 below the record set in the 12 months to June 2010.

Here is a graph of the 12 month running mean to August 2013:

Image

Yes, it has definitely been warm.  The Sub-Tropical Ridge being so far north, and the dry conditions in the northern inland, may have something to do with that too.

The Bureau expects temperatures for the rest of the year to be above average, and claim that

“If a mean temperature of more than 1.0 °C above average is maintained over the next one-, two-, three- or four-month periods, each of the 12-month periods ending September, October, November and December would exceed the previous record from 2005–06 for the warmest 12-month period.”

On the other hand, if  UAH records data for the Australian region of +1.0C for the next four months, the 12 months to December will be +0.748, the warmest calendar year on the UAH record, but still in third position for the 12 month mean.

And there is no doubt that this could happen.  But only in 2006 and 2007 were there a total of just three months out of 12 above +1.0C, not five in a row.  I’m not holding my breath.

It depends which data you would trust, from satellites criss-crossing the globe 24 hours a day, or from 104 scattered stations recording a daily maximum and minimum.

September -December Weather Predictions

September 2, 2013

At the beginning of August my predictions for sub-tropical Queensland (St Lawrence to Longreach and south to the border) for August were:

2-3-4-5-6-7, 9-10-11-12-13, 15-16-17, 19-20-21-22, (24-25-26?) –27-28-29-30.

Results:

There were weather events on August 2, 6-7-8, 12-13-14, 16, 18-19-20 (with some rain on 17th, recorded 18th), 29-30-31.

Predictions were not as good in August, with only 6 out of 8 unequivocal successes, with 1 complete miss and 1 doubtful, and a couple merged together.

Here’s a (rather noisy) plot of August data.Image

I have highlighted changes that matched predictions and the 24-25-26 miss.

I have also indicated with green bars the likely times for weather changes in September.

Predictions for the rest of the year are as published on previous posts.

A vigorous change came through the Capricornia district today, and further events are expected on:  4, 7, 9-10, 13, 16-17-18, 23-24-25, and 30- October 2.

Another update in a month’s time.

PS- Google Chrome solved the problem with uploading images!