Seasonal prediction of blocking frequency: Results from winter ensemble experiments

The patterns which explain the largest fraction of the large-scale variabil ity over the Euro-Atlantic and the Pacific regions are described using the National Centers for Environmental Prediction analysis data. In the descrip tion, special attention is given to the relation between these patterns and local weather regimes. The dynamical characteristics of each regime are fo und to be dependent on its relation with the basic flow over the region of its location. The ability of the European Centre for Medium-Range Weather Forecasts T63L3 1 model in predicting the evolution of these large-scale patterns and assoc iated weather regimes during winter is quantitatively estimated. The skill of the model prediction is shown to depend substantially on the pattern con sidered.