Variability in Skill in 120 h FNOC 500 mb Height Forecasts

The variability of the 120-hr 500-mb height forecasts of the Navy's Operational global model was examind for two winters. The forecasts displayed evidence of marked variability in the quality of forecasts as measured by anomaly correlations computed for the Northern Hemisphere. There were clearly defined periods of good and poor model performance on the time scales of 2-12 days. The role of the flow persistence, the scale of the transient features, the amount and amplitude of eddy activity, and unique synoptic patterns (in contributing to the model performance changes) were considered. None of the above computations could provide an unambiguous indicator of model skill in all cases. The most promising indicator was the transition of the large-scale waves during the integration period. This result is in agreement with Bettge and Baumhefner.