Seasonal Climate Outlook Message for June to September 2008

The bottom line

3 June 2008

The welcome rain at the start of June resulted from an upper level low pressure system that tracked south along the Queensland coast. Some flooding and heavy falls of rain were recorded although largely confined to the coastal strip. For example to date (3 June) Nambour recorded more than 150 mm while inland centres such as Emerald received 45 mm, Roma 23 mm, and Goondiwindi less than 1 mm.

This comes on the back of very dry autumn. Around two thirds of the state recorded below to very much below average rainfall for autumn with a number of locations recording the lowest autumn rainfall on record. This includes Mitchell (recorded 1 mm autumn average 127 mm), Miles (13 mm, autumn average 135 mm), Chinchilla (3 mm, autumn average 138 mm, Urandangi (0 mm autumn average 67 mm) and Oakey (14 mm, autumn average 116 mm).

In the mean time the monthly value of the SOI fell from plus 4.4 for April to minus 3.5 for May. Based on a 'Rapidly Falling' SOI phase and historical rainfall data there is a 20 to 50 % chance of getting above median rainfall throughout most of the state. This represents a shift in the odds towards drier conditions for winter. This does not mean that it will not rain, just that there is a lower probability of getting above median rainfall for June to August.

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

For more information about probabilities, or to find rainfall figures for your area try Rainman Streamflow, available from the DPI&F on 13 23 25.

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 June to August in the following years; 1953, 1957, 1958, 1972, 1999, 2001, 2002 and 2006. Look at your long term average rainfall for June to August and see how many times rainfall was well below, well above or close to average.

The MJO was in Phase 1 (31st May), and while the signal strength has weakened over the past few days, it is still moderate. The active centre of convection is located over the western Indian Ocean near Africa. Currently conditions are suppressed over Indonesia and southern Asia.

The MJO is expected to reach Phase 4 (Maritime Continent) in about 15 days, although most models indicate that signal strength will decrease prior to the MJO's arrival north of Australia. 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)

The full story

Lexie Donald, Qld Climate Change Centre of Excellence, 3 June 2008.

The winter outlook for Queensland shows a moderate shift in the odds towards drier conditions.

Conditions are now Neutral and the La Nina is over. The La Nina weakened over autumn when the existing ENSO pattern traditionally breaks down.

The SOI fell from plus 4.4 in April to minus 3.5 for May. Based on this shift in monthly SOI values the SOI is in a "Rapidly Falling" phase - Phase 3.

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

For much Queensland there is a 20 to 50 % chance of exceeding median rainfall. However, along the Great Dividing Range from CQ to NQ and into the Gulf regions has a higher 50 to 70 % chance of exceeding their June to August 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, this does not mean there will be no rain, just that there is a low chance of exceeding the median winter rainfall.

For example during June through to August Kingaroy and Roma have an 80% chance of getting at least 60 mm, St George has an 65 % chance of at least 60 mm, Jondaryan has an 85% chance of getting at least 40 mm, and Emerald a 75% chance of getting at least 40mm.

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 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 June to August in the following years: in the following years; 1953, 1957, 1958, 1972, 1999, 2001, 2002 and 2006.

Find out your average rainfall for June to August, 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 1 (31st May), and while the signal strength has weakened over the past few days, it is still moderate. Provisional indications suggest the MJO reached Phase 2 on June 2nd. The active centre of convection is located over the western Indian Ocean near Africa. Currently conditions are suppressed over Indonesia and southern Asia.

The MJO is expected to reach Phase 4 (Maritime Continent) in about 15 days, although most models indicate that signal strength will decrease prior to the MJO's arrival north of Australia. 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). 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/ SST pattern conditions are considered to be Neutral, and the SOI has been dropping.

The La Nina has broken down but some aspects remain in place. For example, central equatorial Pacific Ocean temperatures have warmed slightly but remain cooler than normal and cloudiness near the date line remains below 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/.