Seasonal Climate Outlook Message for May to August 2006

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Autumn Crucial Time 12th May 2005 Climate scientists consider this time of year critical in terms of climate patterns that may set in for the next 9 to 12 months. This is because the Pacific Ocean tends to 'lock-in' from one year to the autumn of the following year making the next couple of months the key time to watch for developing trends in both the SOI and sea surface temperatures (SST). At this stage there does not seem to be any sign of an El Nino developing which is positive. However it is also noteworthy that Pacific Ocean sea surface temperatures are no longer reflecting the small La Nina pattern of the last few months. The output of the ocean or coupled ocean/atmosphere forecast models seems to reflect this as the majority indicate the continuation of a neutral sea surface temperature pattern. For more on conditions in the Pacific try the Bureau of Meteorology at www.bom.gov.au/climate/ahead/ The monthly value of the SOI for March was plus 11.4 and for April was plus 13.0 placing the SOI in a 'Consistently Positive' phase. An analysis of a Consistently Positive SOI phase and historical rainfall records indicates a 60 to 70% chance of getting above the long term May to July median rainfall for the Gulf Country, a 50 to 60% chance of getting above the long term May to July median rainfall for southwest Queensland and a 40 to 50% chance of getting above the long term May to July median rainfall for the rest of the state. The last time the SOI phase for April was in a Consistently Positive Phase was in 2000. It will be interesting to see if these positive values persist or drop back to negative or near zero values as has been the case over the last few years. Sustained positive monthly SOI values (>2months) would help provide the basis for an improvement in seasonal conditions. As of the 12th May the 30-day median of the SOI had fallen to plus 4.6. The latest rainfall probability maps are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au and daily updates on the SOI are available on (07) 46881439. Generally for southern NSW, Victoria, the eastern half of South Australia and Tasmania and the southern half of Western Australia there is a 50 to 70% chance of getting above the long term May to July median rainfall. For the rest of Australia the chance of getting above the long term May to July median rainfall is between 30 to 50%. For more information refer to Rainman StreamFlow. This forecast does not indicate the potential distribution or expected timing of rainfall over this period. The forecast is for a full three-month period and does not suggest that any expected rain will fall evenly across these three months. 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 May to July in the following years since 1900 that have had a 'Consistently Positive' SOI phase at the end of April; 2000, 1996, 1975, 1974, 1971, 1964, 1963, 1960, 1959, 1956, 1950, 1939, 1935, 1931, 1928, 1927, 1925, 1923, 1917, 1910, 1903, 1902 and 1901. For example at Miles, below median rainfall for May to July in those years was recorded five times, close to median rainfall was recorded twelve times and above median rainfall was six times. Therefore rainfall at Miles during May to July is more likely to be close to median than well above or below median. For more information refer to Rainman StreamFlow. The last two active phases of the MJO over north Australia occurred in relatively quick succession during late March/early April and then again in late April. As of the 10th May the MJO was in Phase 8 (Western Hemisphere and Africa). The MJO would therefore be next expected across northern Australia around the end of the May. 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 (but not amounts). For more information try www.apsru.gov.au/mjo/ or http://www.bom.gov.au/climate/tropnote/tropnote.shtml As with any probability based forecast system it is important to consider the opposite aspect. For example, Taroom has a 75% chance of getting at least 60 mm during May to July. This also means that there is a 25% chance of NOT getting at least 60 mm during May to July. Another way of looking at this is that in around 7 times out of 10 with the current SOI pattern, Taroom has received more than 60 mm during May to July. Therefore around 3 times out of 10 with the current SOI pattern, Taroom has received less than 60 mm over May to July. When looking at rainfall probabilities for your area it may make it easier to think of them in these terms: 1. Probabilities above 80% highlight a high chance 2. Probabilities above 60% highlight an above median chance 3. Probabilities below 40% highlight a below median chance 4. Probabilities below 20% have a low chance 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. An interesting site http://www.managingclimate.gov.au/ from the 'Climate Variability In Agriculture' (CVAP) research and development program is well worth looking at. It highlights some case studies on how producers and businesses have used (to varying levels of success) climate and weather information in their decision-making processes.