Values of the Southern Oscillation Index (SOI) have remained quite positive over the last two months (November +12.4, December +22.2). According to the SOI Phase system, this places 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 December, the probability of above-median rainfall for the next three-month period (January to March) is between 50 to 70 per cent throughout most of Queensland, which is higher than normal (50 percent).
In assessing this information, it is worth considering other years with a ‘Consistently Positive’ SOI phase at the end of December. Since 1950, these include: 1950, 1955, 1959, 1960, 1961, 1970, 1973, 1975, 1988, 1998, 1999, 2000, 2007, 2008 and 2010.
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 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 the Queensland Climate Change Centre of Excellence.
Further seasonal climate outlook information is available at www.bom.gov.au.