Commentary on rainfall probabilities based on phases of the SOI
Seasonal climate outlook message for December 2013 to February 2014
Commentary on rainfall probabilities based on 'phases' of the SOI
The monthly value of the Southern Oscillation Index (SOI) was -2.1 for October and +10.1 for November. According to the SOI Phase system, this places the SOI in a ‘Rapidly Rising’ phase.
Based on previous years when the SOI has been in a ‘Rapidly Rising’ phase at the end of November, the probability of above-median rainfall for the next three-month period (December to February) is 40 to 60 per cent for most of Queensland. However, probabilities are lower for parts of the north and east of the state and higher for parts of the south-west of the state.
Previous years with a ‘Rapidly Rising’ SOI phase at the end of November include 1906, 1912, 1918, 1934, 1946, 1947, 1959, 1960, 1969, 1973, 1976, 1981, 1984, 1993, 2001 and 2006. The rainfall probabilities stated above are based on the 1900 to 1998 period and do not include 2001 and 2006.
When using a climate outlook it should be remembered that the probability, or per cent 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 Department of Science, Information Technology, Innovation and the Arts.
Further seasonal climate outlook information is available at www.bom.gov.au
Last updated 18 March 2011