Long Paddock

Commentary on rainfall probabilities based on phases of the SOI

Previous commentary

Seasonal climate outlook message for April to June 2016

The monthly value of the Southern Oscillation Index (SOI) was -19.1 in February and -6.3 in March. According to the SOI Phase system, the SOI is in a ‘Consistently Negative’ phase.

A map showing the probability of above-median rainfall for the next three-month period (April to June) is available. This map is based on previous years from 1900 to 1998 which, like 2016, had a consistently negative SOI over February and March (i.e. 1905, 1906, 1912, 1915, 1919, 1926, 1941, 1978, 1983, 1987, 1992, 1993 and 1998). This map indicates a 50 to 70 per cent probability of above-median rainfall for much of Queensland, with below normal (less than 50 per cent) probabilities of above-median rainfall for some northern areas. However, it is difficult to draw meaningful statistics from this information, as at this time of year the SOI is less reliable as an indicator of rainfall for the autumn season.

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

Seasonal climate outlook