Seasonal Climate Outlook Message for March to June 2008

The full story

The seasonal outlook for Queensland remains quite positive. Compared to this time for the past several years, there has been reasonable summer rainfall (and flooding!) in many areas of Queensland. Also compared to recent years there has been a moderate to strong shift of the probabilities towards a wetter outlook over the summer to autumn period. This has been reflected over the past few months or so with the extensive rain and flooding.

In autumn (March) the existing ENSO pattern traditionally breaks down. At the moment however the La Nina remains in place with the central equatorial Pacific waters still cooler than normal, and trade winds enhanced. In addition, climate models indicate that the La Nina pattern will not break down for a few more months, and the SOI is strongly positive.

Based on a shift in monthly SOI values from plus 12.7 in January to plus 21.0 during February 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 west of the state only have a 30 to 50 % chance of above median rainfall.

Queensland receives much of its rain during the summer but as summer ends and autumn begins there is still some chance of getting useful rainfall.

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 55 mm, Jondaryan has a 90% chance of getting at least 60 mm, and Roma, Emerald and St George have a 90% chance of getting at least 40 mm.

A 'Near Zero' SOI phase around September (like last year) is associated with an increased chance of hail and thunderstorm activity throughout northern NSW and southern Queensland over all of summer. This is due to the increased instability of the middle atmosphere (600mb to 500mb) combined with cool air at those levels.

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 March to May in the following years: 1951, 1956, 1963, 1967, 1972, 1974, 1976, 1989, 1999, and 2001.

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 currently in Phase 1 (5th March). The monsoon trough developed with the last two passages of the MJO and should re-develop when the MJO next reaches the Maritime Continent (Phases 4 -5) in about 14 to 20 days. Northern Australia can expect MJO enhanced rainfall probabilities Phases 4 through to 7 during summer. As expected in a La Nina year, the suppressed phases of the MJO are not as defined this summer.

The past three MJO's have lingered in the western Pacific, after a rapid progression eastward over the Indian Ocean basin. This is most likely due to the La Nina atmospheric signature in the western Pacific. The next passage of the MJO (Phase 4, due mid to late March) may well behave in a similar manner if the La Nina pattern remains in place.

At this time of year the MJO is typically associated with the Australian monsoon and increased rainfall over much of Northern Australian and also with features such as tropical cyclones. Several tropical cyclones and tropical lows have/are developing with this passage of the MJO through the tropics north of Australia.

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 (summer) 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.

For example, central equatorial Pacific Ocean temperatures have continued cool and the SOI has remained strongly positive. South east trade wind anomalies have been maintained.

While the mid-Pacific basin remains cool, a patch of warmer water continues to develop in the western Pacific, and this will probably propagate to the east, gradually breaking 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/.