Seasonal Climate Outlook Message for March to June 2009

The bottom line

SOI Remains Consistently Positive. Dave McRae, Qld Climate Change Centre Of Excellence, 04/03/09.

The monthly value of the SOI for January was plus 8.2 and for February was plus 15.2. This places the SOI in a Consistently Positive phase for the 6th month in a row. Based on historical rainfall records and a Consistently Positive SOI phase at the end of February, there is a reasonable 50 to 70% chance of getting above median rainfall during March through to the end of May across most of Queensland.

For example Nambour has an 70% chance of getting above its March to May median rainfall of 485mm, Prairie has a 70% chance of getting above its March to May median rainfall of 76mm, Alpha has a 65% chance of getting above its March to May median rainfall of 98mm, Barcaldine has a 65% chance of getting above its March to May median rainfall of 98mm, Dalby has a 60% chance of getting above its March to May median rainfall of 120mm, Longreach has a 60% chance of getting above its March to May median rainfall of 77mm, Roma has a 55% chance of getting above its March to May median rainfall of 118mm and Macalister has a 50% chance of getting above its March to May median rainfall of 130mm.

For more information on historical rainfall data for your region try Rainman Streamflow or www.bom.gov.au

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%.

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). Therefore users of the SOI and any other seasonal forecasts are urged to investigate skill level for their location by using such tools as 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 March to May in the following years since 1950 that have had a Consistently Positive SOI phase at the end of February; 1951, 1956, 1963, 1967, 1972, 1974, 1976, 1989, 1999, 2001 and 2008. Find out your average rainfall for March to May and see how many times rainfall was well below, well above or close to average during March to May in the listed years.

The 30 day average of the SOI as of 2 March is plus 13.3. You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459.

According to the latest Bureau of Meteorology ENSO Wrap-Up (available at www.bom.gov.au/climate/enso) a neutral sea surface temperature (SST) pattern continues to persist in the Pacific Ocean. This is reflected in the output from the reviewed dynamic climate models which has the majority forecasting a neutral SST pattern to persist through to the end of the June 2009. This is despite some atmospheric indicators such as south east trade winds and SOI indicating borderline La Nina conditions over recent months. For example, the south east trade winds have been stronger than normal across the western half of the equatorial Pacific. This has contributed to the SOI remaining in positive values and the inflow of warm moist air across the eastern Australian coastline.

As autumn is a key time for the establishment of climate phenomena such as El Nino and La Nina, QCCCE climate staff will continue to closely monitor what happens over the next few months.

The Bureau of Meteorology has recently released the climate summary for summer (December 2008 to February 2009). Wetter than average conditions were experienced throughout much of the northern tropics, while drier than average conditions were experienced throughout much of southern Australia. Temperatures also matched this pattern with cooler than average temperatures experienced across northern Australia and warmer than average conditions experienced across southern Australia.

According to the Bureau, rainfall area-averaged across Queensland for summer was the 6th highest on record based on figures since 1900. It is worth noting however that this is a result of well above average rainfall events across the northern half of the state. Rainfall recorded across most of the southern half of Queensland for summer was below average to average. For example, Oakey on the Darling Downs recorded 108mm for summer. This compares to its long term summer average of 252mm. Another way of looking at this is that Oakey only recorded 43% of its average summer rainfall.

The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.

The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. If its timing remains consistent, the next passage of the MJO is likely to occur during early to mid March. Interestingly a key time to watch for the potential development of cyclones is after summer passages of the MJO.

The 8th Australian Tropical Pastures Conference is on the 18th to 19th March, 2009 at Goondiwindi. The theme is Pastures for Production, Soil Health and Carbon Sequestration. For more information on the conference contact Ian Partridge on (07) 46881375 or try the web site at www.tropicalgrasslands.asn.au

When I'm asked about how climate information can be used I refer to a couple of key points developed from client feedback. Key points 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 PIECE OF INFORMATION (SUCH AS A CLIMATE FORECAST).

Forecasts as well do not always give a strong signal as to likely conditions for your location. In assessing climate forecasts as a management tool consider the level of signal for the key decision times in your location. Rainman StreamFlow is a useful tool for this.