Seasonal climate outlook message for December 2023 to February 2024

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

This commentary is based solely on output from the SOI Phase system, which uses a statistical analysis of phases of the Southern Oscillation Index (SOI) and historical rainfall, to indicate whether rainfall over the coming three-month period is likely to be above or below the long-term median. There are five phases of the SOI, which were defined by Dr Roger Stone using a statistical technique (cluster analysis) to group all sequential two-month pairs of the SOI (from 1882 to 1991) into five clusters (click for more detail).

SOI* values for the most recent two months are -6.6 for October and -8.4 for November. Although these values of the SOI are somewhat negative, according to the SOI Phase system, the SOI Phase system has classified the current phase as ‘Consistently Near Zero’.

A map showing the probability of exceeding median rainfall for the next three-month period (December to February) based on a 'Consistently Near Zero’ phase of the SOI over October and November is available. This map is based on 35 previous years from 1889 to 2015 which, like 2023, had a ‘Consistently Near Zero’ phase of the SOI for November (i.e. 1890, 1891, 1895, 1898, 1902, 1903, 1907, 1920, 1926, 1927, 1930, 1931, 1932, 1937, 1945, 1952, 1953, 1954, 1958, 1966, 1967, 1968, 1978, 1979, 1980, 1983, 1985, 1987, 1990, 1995, 1996, 2002, 2003, 2004 and 2012). This map indicates a 40 to 60 per cent (near-average) probability of exceeding median December to February rainfall for most of Queensland.

The current classification of the SOI phase (‘Consistently Near-Zero’) is quite borderline. However, a slightly more negative value of the SOI in either October or November would have resulted in a ‘Consistently Negative’ phase, with a 20 to 40 percent probability of exceeding median December to February rainfall for much of northern and eastern Queensland.

Readers should note that seasonal outlooks are stated in terms of probabilities. For example, whilst an outlook may be stated as ‘a 20 to 40 per cent probability of exceeding median rainfall’, such a statement should be interpreted as also meaning a 60 to 80 per cent probability of below-median rainfall. In cases where outcomes with a high probability may be more likely, this does not mean that less probable events will not occur in any given year.

Rainfall probabilities produced by the SOI Phase system may differ from those produced for the same period by other climate outlook schemes, due to the different methodologies used. 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. 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.

The Science Division of the Department of Environment and Science (DES) provides outlooks for the summer period (November to March). The outlooks for summer rainfall are based on conditions leading up to summer, including the state of the El Niño–Southern Oscillation (ENSO) phenomenon and factors which alter the impact of ENSO on Queensland rainfall (i.e., the more slowly changing extra-tropical sea-surface temperature pattern in the Pacific Ocean). The DES Monthly Climate Statement for December 2023 is now available.

 

^{* www.longpaddock.qld.gov.au/soi/soi-data-files (monthly SOI 1887-1989 base period)}