Seasonal Climate Outlook Message for April to July 2011

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

The Southern Oscillation Index (SOI) remains extremely positive, with monthly values of the index decreasing slightly from +22.6 in February to +17.5 in March. These values currently place the SOI in a Consistently Positive Phase, now the eighth consecutive month in this phase.

The Queensland Climate Change Centre of Excellence (the Centre) considers that, at this time of year, the Southern Oscillation Index (SOI) or other measures of the El Niño-Southern Oscillation (ENSO) are less reliable as indicators of rainfall for the autumn season.  However, based on previous years when the SOI has been in a 'Consistently Positive' phase at the end of March, there is a 50 to 70% probability that rainfall during April to June will be above the long-term median throughout much of Queensland.

In assessing this information, it is worth considering other years with a ‘Consistently Positive’ SOI phase at the end of March. Since 1950, these include: 1950, 1956, 1967, 1971, 1974, 1975, 1976, 1989, 1999, 2000, 2001, 2004 and 2008.

When using a climate forecast 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% probability of above-median rainfall, then there is also a 30% chance of below-median rainfall. It does not mean that rainfall will be 70% 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. Further seasonal climate outlook information is available at www.longpaddock.qld.gov.au and www.bom.gov.au