Seasonal Climate Outlook Message for September to December 2008

The full story

The Full Story

8 September 2008.

A neutral ENSO pattern is now firmly established and is likely to continue throughout 2008. There is now only a relatively minor possibility of an El Nino developing, and if so it would evolve later in the year.

The winter outlook for Queensland shows a marginal shift in the odds towards wetter conditions as a result of the SOI rising to plus 2.3 for July to plus 8.0 for August. Based on the shift in monthly SOI values the SOI is in a "Rapidly Rising" phase - Phase 4.

Based on this SOI Phase and historical rainfall records much of Queensland has a 40 to 70 % chance of exceeding median rainfall. The exception is for a region in the south west of the state where there is a lower 20 to 50% chance of exceeding their median rainfall.

Further analysis indicates that the September to November rainfall is likely to be close to or above average (middle to upper third) rather than below normal (lower third). This represents a slight shift in the odds towards wetter conditions compared with last months outlook.

For example Longreach has a 70% chance of getting above its September to November median rainfall of 42 mm, and Emerald and Gympie have a 55% chance of getting above their September to November median rainfall of 111 mm and 196 mm respectively. Roma has a 48% chance of getting above its September to November median rainfall of 124 mm while Charter Towers has a 73% chance of getting above its September to November median rainfall of 63 mm.For more on rainfall probabilities for your location refer to "Rainman StreamFlow".

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 30% chance of recording more than 100 mm then there is also a 70% chance of recording less than 100 mm i.e. 30-70; 70-30. It does not mean that you will get 30% more than 100 mm or 100 mm plus another 30%.

For those who like to follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during September to November in the following years since 1950: 1954, 1962, 1964, 1966, 1967, 1970, 1971, 1983, 1985, 2000 and 2007. Find out your average rainfall for July to September and see how many times rainfall was well below, well above or close to average during September to November in the listed years.

The SOI is simply a measure of the difference in barometric air pressure between Darwin and Tahiti. It typically ranges in value from plus 30 to minus 30.

Changes in sea surface temperature (SST) patterns in the central Pacific drive changes in the global circulation patterns and influence our local climate. Although the SOI is measured on a daily basis, it is the shift in value of the SOI from month to month that reflects SST patterns and the strength of the Walker Circulation.

By using a statistical analysis of SOI phases and historical climate data (rainfall, frost, hail, temperature, etc), a forecast can be developed to indicate for example, whether the coming three months are likely to be wetter or drier than normal.

It is worth noting that the SOI influence on climate varies across Australia (greatest skill is for eastern Australia) and between seasons (usually greatest skill is for winter, spring and early summer).

Generally, periods of widespread pro-longed drought, especially across eastern Australia, are associated with Consistently Negative SOI phases (average monthly values of the SOI below minus 5.0 and often an El Niño SST pattern). This negative value is a reflection of barometric air pressures over northern Australia being higher than those in the central Pacific. This may slow or stop the flow of the south-east trade winds as well as reduce the occurrence of rain depressions (and cyclones).

For those interested, updates of 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 was in Phase 4 (8th September) after the signal being incoherent and weak through July and up to mid-August. This indicates that the MJO is located to the north of Australia, about the Maritime Continent. Provisional indications suggest the MJO will reach Phase 4 mid to late October

During spring Queensland can expect enhanced chances of rainfall Phases 6 and 7 (NQ), and Phase 5 (S and SWQ). The MJO suppresses the chances of rain during spring in Phases 1 and 2. Check the Bureau of Meteorology's MJO page and go to 'seasonal composites' for more details.

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/ .Neutral SST conditions and ENSO pattern are firmly established, and the SOI for June was positive.

Central equatorial Pacific Ocean sea surface temperatures are near normal, and slightly cooler at the sub-surface. Sea surface temperatures in the eastern equatorial Pacific Ocean are somewhat warmer than normal. Cloudiness near the date line is near normal and the trade winds average to above average.

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/.

Last updated: 7 September 2008