Commentary on rainfall probabilities based on phases of the SOI
Seasonal climate outlook message for November 2015 to January 2016
The monthly value of the Southern Oscillation Index (SOI) was -16.7 in September and -21.3 in October. According to the SOI Phase system, the SOI remains in a ‘Consistently Negative’ phase.
Based on previous years when the SOI has been in a ‘Consistently Negative’ phase at the end of October, the probability of above-median rainfall for the next three-month period (November to January) is less than 30 per cent for most northern and eastern parts of Queensland. However, the probability of exceeding median rainfall is marginally higher (30 to 60 per cent) for many western and some southern parts of the state.
Previous years with a ‘Consistently Negative’ SOI phase at the end of October include 1900, 1901, 1902, 1911, 1913, 1914, 1923, 1932, 1939, 1940, 1946, 1951, 1965, 1969, 1972, 1977, 1982, 1987, 1991, 1993, 1994, 1997 and 2002. The rainfall probabilities stated above are based on the 1900 to 1998 period (that does not include 2002).
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 should note that, while climate outlook schemes cannot provide outlooks with absolute certainty, users who follow a skilful scheme should benefit from doing so in the long-term. Thus, users should consider the historical track record of any scheme, and such information is becoming increasingly available.
Further seasonal climate outlook information for Queensland is available in the monthly climate statement produced by the Department of Science, Information Technology and Innovation.
Last updated 18 March 2011