Experimental long-range (monthly) weather forecasts were prepared, for internal assessment, within the Bureau from 1954 to 1971. These were based on an apparent tendency for certain patterns of anticyclonicity to persist for up to a season or longer. An Extended Period Forecasting Section was established as an operational unit of the Bureau in the late 1960s. While its main concern was the regular issue of forecasts up to four days ahead, experimental 30-day forecasts were prepared. These were based on an extension of the methods used in four-day forecasting; a zonal index cycle, blocking patterns, persistence, and the movement of large-scale anomalies. The forecasts were not issued to the public. An analysis of the forecasts revealed that rainfall forecasts were no more accurate than would be expected from chance. Temperature forecasts were slightly (and significantly) more accurate than chance, but not sufficiently accurate to be useful. The experiment was discontinued in 1971.

By the early-1980s, attention had returned to the possible use of the El Niņo—Southern Oscillation in prediction. Work on the physical cause of the phenomenon had commenced, and several papers describing patterns and relationships between the El Niņo—Southern Oscillation, sea-surface temperature and Australian climate had been published (e.g., Priestley 1964; Pittock 1975; Streten 1981; Coughlan 1979). Some of the earlier (e.g., Quayle) lag relationships had been validated and extended using new data (Nicholls and Woodcock 1981; McBride and Nicholls 1983). New relationships indicating that seasonal temperature, wet-season onset, and even seasonal tropical cyclone activity were predictable, through the El Niņo—Southern Oscillation, had been uncovered (Nicholls 1978, 1979; Nicholls et al. 1982). The recognition in mid-1982 that a major El Niņo episode was underway led to cautious statements regarding possible implications for Australian rainfall through the remainder of 1982, based on this work (Nicholls 1983). The Bureau's National Climate Centre began preparing and testing monthly Seasonal Climate Outlooks in 1988, and issuing them publicly in 1989.

Simple linear lagged regression, and variants on this, between the SOI (the Southern Oscillation Index, an index of the difference in pressure between Tahiti and Darwin, and a simple measure of the El Niņo—Southern Oscillation) and subsequent rainfall provide the basis for the Seasonal Climate Outlooks. Trends and phases (Zhang and Casey 1992; Stone and Auliciems 1992) of the SOI are taken into account (since 1995), as are some patterns of sea-surface temperature (since 1996). The various predictions are combined in a statistically optimal fashion (Casey 1995). Sophisticated time-series methods developed in BMRC (Drosdowsky 1996) are also used to project the SOI into the future. These projections can then be used to find analogues, i.e., years when the SOI has behaved similarly to the current year. Detailed meteorological data from these analogue years can then be used, for instance, in crop models to examine likely crop yields. By the mid-1980s it was clear that the SOI could be used to produce predictions not just of climate variations, but also of the impact of these variations on the Australian economy and ecology (Nicholls 1988).

Bureau of Meteorology