Seasonal Climate Outlook Message for August to November 2007

The full story

Rain Welcome Dave McRae. 23/08/07

An upper trough over central Queensland and small low pressure system off the south east Queensland coast helped trigger some useful and timely rain during the middle of the month. While useful for crops and pastures a lot more is needed before 'drought breaking' rainfall is recorded. To look at the latest weather observations for Queensland go to www.bom.gov.au/weather/qld/observations

In contrast to rainfall probabilities for July to September, there has been a drop in the chance of getting median rainfall for August to October throughout Queensland. Hopefully this is only a temporary pattern. Coming after a particularly dry July though it is still of some concern. It is also worth noting that we are still in our 'dry season' and that August and September have the lowest median monthly rainfall totals for most locations in Queensland. Therefore while not impossible, it would be considered unusual to record 'drought breaking' rain during those two months regardless of the seasonal outlook.

Since the start of the August the 30day average of the SOI has trended marginally upwards and as of the 22nd August is plus 1.9. It would be helpful to our spring/summer outlook if the SOI went into a 'Consistently Positive' SOI phase and remained there for a number of months. The last time the SOI was in a "Consistently Positive" phase for more than one month was from September 2000 to March 2001. Daily updates on the SOI are available on (07) 46881439 or at www.longpaddock.qld.gov.au You can also receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service call (07) 46881459.

When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example if there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%. For more on rainfall probabilities for your location refer to Rainman StreamFlow.

A weak MJO crossed to the north of Australia in the first week of the month. Therefore it is surprising to see an active phase of the MJO currently developing in the Indian Ocean. While still only weak if it continues to develop we could see the next passage of the MJO cross to the north of Australia much earlier than expected in 7 to 14 days. At this time of year the MJO is typically associated with monsoonal bursts over India and eastern Asia, and tropical storms, cyclones and typhoons in the South China Sea and northern western Pacific Ocean. We would usually expect to see a greater impact on our rainfall (northern Australia) during our spring and summer.

The MJO is a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events (but not amounts). For more information try www.apsru.gov.au/mjo/

Only parts of south west Queensland recorded near average minimum temperatures during July. According to the Bureau of Meteorology, minimum temperatures during July were 1 to 2 degrees below average throughout most of Queensland with the exception of coastal Queensland where minimum temperatures were 2 to 4 degrees below average for July. The coldest night was minus 8.8°C at Stanthorpe on the 19th and the warmest nights were 24.3°C at Coconut Island on the 9th and 20th, and at Horn Island on the 26th. Maximum temperatures for July were also 1 to 2 degrees below average throughout central and northern Queensland but close to average throughout southwest and southern Queensland.

Most of Queensland recorded below average rainfall for the month with a number of locations recording the lowest on record. These included Mt Isa, Mackay, Rockhampton, Tambo and Oakey. For the latest climate summaries go to www.bom.gov.au/climate

To follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during August to October in the following years 1918, 1923, 1925, 1937, 1951, 1965, 1970 and 1976. Find out your average rainfall for August to October and see how many times rainfall was well below, well above or close to average during August to October in the listed years.

According to the Bureau of Meteorology in their "ENSO Wrap-up" available at www.bom.gov.au the past three months have seen conditions in the Pacific Ocean fluctuate without any consistent trend towards either a La Nina or El Nino being apparent. For example during July there where periods of weakening and strengthening south east trade Winds, falling and rising SOI values (30day average of the SOI value varied from +4.2 to -11.9) and warming and cooling ocean temperatures. So while the latest runs from the computer models continues to indicate a reasonable chance for a La Nina to develop in 2007, there needs to be some changes in our climate indicators. This would include consistently stronger than average south east trade winds, positive SOI values and further cooling of the eastern equatorial Pacific Ocean. It is also starting to get late in the year for a La Nina to develop.

In very general terms a La Nina event has the potential in increase rainfall over Australia, Papua New Guinea, Indonesia, New Zealand, India, Thailand, southern Africa, the Sahel and Central America. This type of pattern has the potential to reduce rainfall over parts of Europe, the United States and parts of Central Asia and South America.

When I'm asked about how climate information can be used I refer to a couple of key points developed from client feedback. Key points include that management decisions should never be based entirely on one factor such as a climate or weather forecast. As always, everything that could impact of the outcome of a decision (soil moisture, pasture type/availability, crop and commodity prices, machinery, finance, costs etc) should be considered. For example, the level of soil moisture at planting is the major factor influencing crop yield or success.

A simple cost benefit analysis when making a major decision may also be useful. For example what will I gain if I get the desired outcome? What will I lose (sleep, money, family relationships) if I do not get the desired outcome and what other options (risk neutral) are there? A PART OF THIS PROCESS IS TO HELP MANAGERS TO BE CAREFUL NOT TO CHANGE FROM NORMAL RISK MANAGEMENT TO HIGH LEVEL RISK TAKING BASED ON A PIECE OF INFORMATION (SUCH AS A CLIMATE FORECAST).

The Climate Variability In Agriculture' (CVAP) program has an interesting site which highlights some case studies on how producers and businesses have used climate and weather information in their decision-making processes at http://www.managingclimate.gov.au/