Skill of monthly forecasts during the Northern Hemisphere summer

We have performed GCM experiments using the National Meteorological Center's Medium Range Forecasting (MRF) model to study the skill of monthly forecasts during the Northern Hemisphere summer and to test the impact of sea surface temperature anomalies (SSTAs) on such forecasts. The daily skill varies a great deal. The skillful daily forecasts last from 5 to 8 days for the Southern Hemisphere and from 6 to 8 days for the Northern Hemisphere. SSTAs have positive impact on the forecasts in the tropics and surface variables, but the impact of tropical SSTAs on the extra-tropical circulation is, in general, positive but small. Overall, the initial conditions play a more important role than SSTAs in determining the forecast skill.