Seasonal Climate Outlook Message for December 2010 to March 2011

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

Historically, when the SOI has been in a 'Consistently Positive' phase at the end of November, 60 to 80% of the time rainfall has been above the long-term median throughout much of eastern Queensland (east of a line running from the bottom of the Gulf of Carpentaria through to the western Darling Downs) during December to February. Throughout the rest of the state rainfall has been above the long-term median only 40 to 60% of the time.

The probability of receiving above-median rainfall varies from location to location.  For example, based on a ‘Consistently Positive’ SOI phase at the end of November, there is an 80% probability of Monto receiving above median December to February rainfall (288mm).  For the same period there is a 74% probability of Charters Towers receiving above median rainfall (337mm), a 75% probability of Yuleba receiving above-median rainfall (227mm), and a 55% probability of Longreach receiving above-median rainfall (190mm).

The last time there was a Consistently Positive SOI phase at the end of November was in 2008. Other years since 1950 that have had the same SOI phase at the end of November include: 1950, 1955, 1961, 1962, 1964, 1970, 1971, 1975, 1988, 1998, 1999, 2000 and 2007.

When using a climate forecast you should remember 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.