Two analogue or phase selection methods are regularly examined, but not officially included, in the Seasonal Climate Outlook (SCO) issued by the National Climate Centre; the non-linear Southern Oscillation Index (SOI) analogue developed by Drosdowsky (1994), and the SOI phase system of Stone and Auliciems (1992). An SST phase classification system, similar to that of Stone and Auliciems has been developed based on the two leading modes of Indian / Pacific Ocean variability. The hindcast skill of these three systems in predicting seasonal rainfall with a one month lead is examined using a cross-validation methodology, and compared with the current operational discriminant analysis forecast system. All systems have similar levels of hindcast skill and could potentially be combined to produce a system with a higher level of skill than that of any individual system.
Wasyl Drosdowsky (Thu,) studied this question.