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Commentary on rainfall probabilities based on phases of the SOI

Previous commentary

Seasonal climate outlook message for February to April 2017

The monthly value of the Southern Oscillation Index (SOI) was +0.4 for December and +0.5 for January. According to the SOI Phase system, the SOI is in a ‘Consistently Near-Zero’ phase.

A map showing the probability of above-median rainfall for the next three-month period (February to April) is available. This map is based on previous years from 1900 to 1998 which, like 2017, had a ‘Consistently Near-Zero’ phase of the SOI for January (i.e. 1900, 1903, 1907, 1908, 1909, 1910, 1924, 1925, 1927, 1932, 1936, 1945, 1947, 1948, 1949, 1960, 1965, 1966, 1972, 1975, 1979, 1981, 1984, 1985, 1988, 1990, 1991 and 1994). This map indicates a 40 to 60 per cent (near-normal) probability of above-median February to April rainfall for most of Queensland.

The Department of Science, Information Technology and Innovation (DSITI) provides outlooks for the summer period (November to March) based on conditions leading up to summer, including the state of the El Niño–Southern Oscillation (ENSO) phenomenon prior to summer, and on factors which alter the impact of ENSO on Queensland rainfall (i.e. the more slowly changing extra-tropical sea surface temperature (SST) pattern in the Pacific Ocean). The DSITI Monthly Climate Statement for February 2017 is available.

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 the SOI is less reliable as an indicator of rainfall for the autumn season. 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