Seasonal Climate Outlook Message for January to April 2013

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

The monthly value of the Southern Oscillation Index (SOI) fell from +3.8 in November to -7.4 in December. According to the SOI Phase system, this places the SOI in a ‘Rapidly Falling’ phase.

Based on previous years when the SOI has been in a ‘Rapidly Falling’ phase at the end of December, the probability of above-median rainfall for the next three-month period (January to March) is 50 to 70 per cent for much of Queensland. However, for South East Queensland, the probability of above-median rainfall for January to March is 30 to 50 per cent.

Previous years with a ‘Rapidly Falling’ SOI phase at the end of December include 1908, 1912, 1918, 1934, 1935, 1940, 1943, 1948, 1952, 1972, 1976, 1995, 2001 and 2002. The rainfall probabilities stated above are based on the 1900 to 1998 period and do not include 2001 and 2002.

When using a climate outlook 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 Department of Science, Information Technology, Innovation and the Arts.

Further seasonal climate outlook information is available at www.bom.gov.au