Seasonal Climate Outlook Message for April to July 2008

The full story

The seasonal outlook for autumn for Queensland is quite positive. Compared to this time for the past several years, there has been reasonable summer rainfall in many regions. Also compared to recent years there has been a moderate to strong shift of the probabilities towards a wetter outlook over the autumn to early winter period.

In autumn (March) the existing ENSO pattern traditionally breaks down. At the moment however the La Nina, although weakening with gradually warming equatorial water temperatures, is maintained. In addition, climate models indicate that the La Nina pattern will not break down for a couple more months, and the SOI remains quite positive.

Based on a shift in monthly SOI values from plus 21.0 in February to plus 10.2 during March the SOI is in a "Consistently Positive" phase. Further analysis indicates rainfall for much of Queensland is more likely to be above or close to the long term average (or middle third to upper third) rather than below or well below average.

The chance of getting above median rainfall for much Queensland is a 50 to 70 % chance of exceeding median rainfall. However, some regions in the south and the far west and the north of the state only have a 30 to 50 % chance of above median rainfall. An isolated region adjacent Cooloola and the Sunshine Coast has a 70 to 80 % chance of exceeding their April to June median rainfall. For more details look at the SOI phase maps here on longpaddock.

While these rainfall probabilities may still not be as high as some would like, there is a reasonable chance of getting some autumn rainfall. For example during March to May Kingaroy has an 80% chance of getting at least 80mm, Jondaryan and Roma have an 85% chance of getting at least 40 mm, Emerald and St George have an 80 % chance of at least 60 mm.

When using any probability based forecast you should remember that the probability or percent chance of something occurring is just that - a probability. 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".

To follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during April to June in the following years: 1950, 1956, 1967, 1971, 1974, 1975, 1976, 1989, 1999, 2000, 2001 and 2004.

Find out your average rainfall for March to May, and how many times rainfall was well below, well above or close to average over autumn during those years.

For those interested daily updates on the SOI are available on (07) 4688 1439 or at www.longpaddock.qld.gov.au . You can also receive a text message with the latest SOI values sent to your mobile - just contact me on 4688 1588.

The MJO is weak, but eastward propagation is still evident. The monsoon trough developed with the each passages of the MJO over summer. During autumn the MJO can be expected to increase the chance of rainfall in phases 4, 5 and 6, but not to the same degree as in summer.

Over summer and (early) autumn the passage of the MJO is typically be associated with Southern Hemisphere tropical storms, and also cyclones in the Indian Ocean and western Pacific Ocean. We usually expect to see a greater impact on our rainfall (northern Australia) during our summer and autumn. There is now an increased chance of cyclones to the north of Australia slightly lagging each (early autumn) passage of the MJO.

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. For more information try www.apsru.gov.au/mjo/

According to the Bureau of Meteorology in their "ENSO Wrap-up" available at www.bom.gov.au/climate/enso/ the mature La Nina pattern remains in place, but is beginning to break down.

For example, central equatorial Pacific Ocean temperatures have warmed slightly but remain cooler than normal and the SOI has remained positive. South east trade wind anomalies have been maintained.

While the mid-Pacific basin still remains cooler than normal, a patch of warmer water continues to develop in the western Pacific, and this will probably propagate to the east, and continue to gradually break down the La Nina pattern.

Key points about how climate information is applied have been developed from client feedback. These 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 SINGLE 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/.