Seasonal Climate Outlook Message for November 2008 to February 2009

The bottom line

3rd November 2008.

SOI remains positive

The monthly SOI value remained in moderately strong positive values with a thirty day average of plus 13.7 in September followed by plus 14.2 during October. This SOI indicates a "Consistently Positive" phase (Phase 2) for October.

Based a consistently positive October phase of the SOI and historical rainfall data, there is a 50 to 70% chance of getting at least median rainfall throughout Queensland during November to January.

A more detailed analysis indicates that rainfall is likely to be above average (upper third) rather than average or well below average (middle to lower third).

For example, there is a 52% chance of exceeding the November to January median rainfall of 290 mm at Kingaroy, and there is a 64% chance of exceeding the November to January median rainfall of 159 mm at St George and the November to January median rainfall of 225 mm at Emerald. At Cloncurry there is a 70% chance of exceeding the November to January median rainfall of 168 mm, while Mareeba has a 73% chance of exceeding the November to January median rainfall of 339 mm (Source: Rainman Streamflow).

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 November to January in the following years since 1950: 1955, 1962, 1964, 1970, 1971, 1973, 1974, 1975, 1983, 1988, 1989, 1996, 1998, and 2000. Find out your long-term average rainfall for November to January and see how many times rainfall was well below, well above or close to this average during November to January in the listed years.

According to the latest ENSO wrap up from the Bureau of Meteorology (www.bom.gov.au); sea surface temperatures (SST) in the Pacific Ocean are in a neutral pattern, trade winds remain close to or slightly above average and cloudiness near the international date-line is near normal.

Therefore SST values are most likely to remain in a neutral climate pattern with a low risk of a return to El Nino conditions over summer 2008 - 2009.

As always, when using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example 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%.

The thirty day average of the SOI as of the 4th of November was plus 14.8.

The full story

The Full Story

3rd November 2008.

A neutral ENSO pattern is now firmly established and is very likely to continue throughout summer 2008 - 2009. There is only a very minor possibility of an El Nino developing.

Based on the monthly SOI values of plus 13.7 during September and plus 14.2 in October the SOI is in a "Consistently Positive" phase - Phase2.

Based on this SOI Phase and historical rainfall records much of Queensland has a 50 to 70 % chance of exceeding median rainfall November through January. The exception is areas in the far west of the state (Northern Territory border) that have a lower 40 to 60 % chance of exceeding median rainfall November to January.

Further analysis indicates that the November to January rainfall is likely to be above average (upper third) rather than average or below average (lower to middle thirds). This represents a continuance of the odds towards wetter conditions similar to last months outlook.

For example, there is a 52% chance of exceeding the November to January median rainfall of 290 mm at Kingaroy, and there is a 64% chance of exceeding the November to January median rainfall of 159 mm at St George and the November to January median rainfall of 225 mm at Emerald. At Cloncurry there is a 70% chance of exceeding the November to January median rainfall of 168 mm, while Mareeba has a 73% chance of exceeding the November to January median rainfall of 339 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 November to January in the following years since 1950: 1955, 1962, 1964, 1970, 1971, 1973, 1974, 1975, 1983, 1988, 1989, 1996, 1998, and 2000. Find out your long-term average rainfall for November to January and see how many times rainfall was well below, well above or close to this average during November to January 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 prolonged 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. A summary of the seasonal outlook is available at (07) 4688 1623.

The MJO was in Phase 5 at end of October. This indicates that the MJO is located over the Maritime Continent, about western Indonesia. The MJO signal strength has been well organised for much of September. Provisional indications suggest the MJO will next reach Phase 4 early to mid December.

During summer (Dec- Jan - Feb) Queensland can expect enhanced chances of rainfall Phases 5, 6 and 7. The MJO strongly suppresses the chances of rain during 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 September was positive.

Central equatorial Pacific Ocean sea surface temperatures are near normal, and there are significant sub-surface cooler anomalies. Cloudiness near the date line is near normal and the trade winds are close to average in the eastern equatorial Pacific and stronger than average in the central and western Pacific. Dynamic Climate models forecast continuation of these neutral conditions over the coming summer months through to March 2009.

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: 3 November 2008