This replaces simple persistence as a skill threshold. Multiple least squares regression is employed to test a total of fourteen possible predictors for the selection of the best predictors, based upon 1950-1994 developmental data. A range of zero to four predictors were chosen in developing twelve separate regression models, developed separately for each initial calendar month.
Predictors are the predictands themselves at earlier times.
Final skill estimates reflect levels comparable to those of more sophisticated statistical and dynamical models. These cold phase conditions may give way to neutral ENSO conditions in the summer of 2000. Forecasts all the way back to those issued in late 1998 have consistently called for neutral conditions to prevail in the summer of 2000. The 0 and 1 season lead forecasts in particular have performed very well, being within 0.6 C of the actual anomaly all the way back to those issued in late 1998 with the exception of the DJF 1999-2000 verification. Over the last couple of years the performance of this model has been very competitive with both statistical and numerical ENSO forecast models.