Seasonal Climate Outlook Message for June to September 2012

Commentary on rainfall probabilities based on 'phases' of the SOI

Values of the Southern Oscillation Index (SOI) were -6.2 in April and -2.4 in May. According to the SOI Phase system, this places the SOI in a ‘Consistently Near Zero’ phase.

Based on previous years when the SOI has been in a ‘Consistently Near Zero’ phase at the end of May, the probability of above-median rainfall for the next three-month period (June to August) is between 40 and 60 per cent throughout most of Queensland. A 40 to 60 per cent probability of above- or below-median rainfall means that a ‘Consistently Near Zero’ phase of the SOI, in May, has little bearing on rainfall from June to August.

In assessing this information, it is worth considering other years with a ‘Consistently Near Zero’ SOI phase at the end of May. Since 1950, these include: 1954, 1959, 1966, 1967, 1976, 1982, 1984, 1986, 1996, 2003 and 2007.

When using a climate outlook it should be remembered that the probability, or percent chance, of something occurring is just that – a probability. For example, if there is a 70 per cent probability of above-median rainfall, then there is also a 30 per cent chance of below-median rainfall. It does not mean that rainfall will be 70 per cent more than the median.

Users are advised not to rely on a single climate outlook alone and should consider the range of climate risk assessment information that is available. In the first instance, users in Queensland may wish to consult the monthly climate statement produced by Science Delivery Division.

Further seasonal climate outlook information is available at www.bom.gov.au