Recent trends in the Southern Oscillation Index (SOI) can be used to calculate more accurately the probabilities of receiving particular amounts of rainfall at a particular location; over the next few months. The phases of the SOI were defined by Dr Roger Stone then of QDPI, who used a statistical technique (cluster analysis) to group all sequential two-month pairs of the SOI (from 1882 to 1991) into five clusters (see legend below & help on use of trends in the SOI).
By using this information we have constructed maps of future rainfall probability.
Reference for the SOI Phase system: Stone, R.C., Hammer, G.L and Marcussen, T. (1996) Prediction of global rainfall probabilities using phases of the Southern Oscillation Index. Nature, 384, 252-255.