This replaces simple persistence as a skill threshold. 14 candidate predictors are made available for the selection, based on the 1950-1994 period. Zero to four predictors were chosen for regression models for each of the calendar months.
Predictors are the predictands themselves at earlier times.
Final skill estimates reflect levels comparable to those of more sophisticated statistical and dynamical models. For the short leads, these forecasts are based almost solely upon the persistence of initial conditions. While they underestimated the intensity of the warming that has occurred, they did predict warming. The strength of the warm forecast has increased in parallel with the increases in the observed initial state. The authors wish to thank William Gray, Tony Barnston, John Sheaffer, Dave Enfield, Dennis Mayer, Barb Brumit, Amie Hedstrom, Bill Thorson and Rick Taft for all their help and comments concerning this work.