Seasonal Climate Outlook Message for April to July 2012

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

Values of the Southern Oscillation Index (SOI) have been near-average over the last two months (February +0.8, March +2.3). 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 March, the probability of above-median rainfall for the next three-month period (April to June) is between 40 to 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 March, has no bearing on rainfall from April to June.

In assessing this information, it is worth considering other years with a ‘Consistently Near Zero’ SOI phase at the end of March. Since 1950, these include: 1953, 1954, 1957, 1958, 1962, 1963, 1965, 1972, 1982, 1995, 1996 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.

As the SOI is less reliable as an indicator of rainfall for the autumn season, 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 the Queensland Climate Change Centre of Excellence.

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