Commentary on rainfall probabilities based on phases of the SOI
Seasonal climate outlook message for May to July 2016
The monthly value of the Southern Oscillation Index (SOI) was -6.3 in March and -19.1 in April. According to the SOI Phase system, the SOI is in a ‘Rapidly Falling’ phase.
A map showing the probability of above-median rainfall for the next three-month period (May to July) is available. This map is based on previous years from 1900 to 1998 which, like 2016, had a rapidly falling SOI over March and April (i.e.1909, 1912, 1914, 1922, 1924, 1944, 1945, 1947, 1952, 1965, 1967, 1969, 1976, 1993, 1994, 1995 and 1997). This map indicates a 30 to 50 per cent probability of above-median rainfall for most of Queensland, with above normal (higher than 50 per cent) probabilities of above-median rainfall for parts of the north tropical coast and some south-eastern areas.
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.
Furthermore, 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