Seasonal Climate Outlook Message for February to May 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 falling slightly from +26.4 in December to +18.1 in January. These values currently place the SOI in a Consistently Positive Phase.

Based on previous years when the SOI has been in a 'Consistently Positive' phase at the end of January, there is a 50 to 70% probability that rainfall during February to April 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 January. Since 1950, these include: 1951, 1956, 1957, 1962, 1974, 1976, 1989, 1997, 1999, 2000, 2001, 2008 and 2009.

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.

From a risk management point of view, the SOI-Phase system continues to highlight the potential for further significant rainfall this summer.  While this does not necessarily equate to ongoing flooding, it is a risk that should be monitored.

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