Seasonal Climate Outlook Message for July to October 2008

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The Full Story

6 July 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 late 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 2.9 for June from minus 3.5 in May.

Based on the shift in monthly SOI values the SOI is in a "Rapidly Rising" phase - Phase 4.

For much Queensland there is a 50 to 70 % chance of exceeding median rainfall. The exception is for a region on the central north of the state where there is a lower 30 to 50 % chance of exceeding the July to September median rainfall. However, it is northern Australia's dry season, and there would be little opportunity for pasture growth even if the outlook were stronger. For more details look at the SOI phase maps here on longpaddock.

Further analysis indicates rainfall for much of Queensland is more likely to be close to or above the long term average (or in the middle third to upper third) rather than well below (bottom third) the average.

For example during July through to September Kingaroy and Jondaryan have an 70% chance of getting at least 80 mm, Roma and St George have a 70 % chance of at least 60 mm, and Emerald a 65% chance of getting at least 70mm. 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%.

To follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during July to September in the following years: in the following years; 1966, 1967, 1970, 1973, 1986, 1996, 1998, 2001, 2005, and 2007. Find out your average rainfall for July to September, and how many times rainfall was well below, well above or close to average over autumn during those 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 8 (6th July), fluctuating from Phase 1. This indicates that the last MJO is breaking down somewhere near the date line and that the band over cloud over central Africa, indicative of the next round of MJO activity. Provisional indications suggest the MJO will reach Phase 4 in about 21 days, or late July.

India is now enjoying a vigorous monsoon season, after a good start, about a week earlier than normal. Despite the absence of an active MJO phase in the Indian Ocean at present the monsoon is active in northeastern India, with associated showers in the rest of the country except the far west.

In wintertime Queensland can expect enhanced chances of rainfall Phases 2 and 3 (NQ), Phase 4 (CQ and SEQ) and Phase 5 (S and SWQ). South eastern Australia can expect MJO enhanced chances of rain during Phases 5 and 6. 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 temperatures are near normal, and indeed are near normal across the entire ocean basin. Subsurface warm anomalies have also moderated in the central and western basin, with a weak subsurface warm pool in the east. Cloudiness near the date line is near normal and the trade winds about 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: 6 July 2008