THE PERFORMANCE OF 4 GLOBAL-MODELS OVER THE AUSTRALIAN REGION

National weather services now receive global model forecasts from a nu mber of centers around the world. The existence of these forecasts rai ses the general question of how the operational forecaster can best us e the information that the ensemble of predictions provides. The Austr alian Bureau of Meteorology receives four global model forecasts in re al-time, but at present their performance is evaluated almost entirely in a subjective manner. In this study, in addition to the standard ob jective measures (for example, bias and rms error), several alternativ e objective measures of model performance are calculated (such as the temporal forecast consistency of a given model and divergence between different models), in an attempt to provide the forecasters with more effective tools for model assessment. Both kinds of measures are appli ed to a two-year dataset (October 1989 to September 1991) of daily sea level pressure predictions from the four models. There are two main o utcomes of this study. First, the current subjective system of ranking the various models has been augmented with more objectively based per formance measures. Second, these performance statistics provide guidan ce to the operational forecasters in a number of ways: geographical re gions with large systematic errors can be identified for each model; c ase studies are presented that illustrate the utility of the regional maps of bias, consistency, and divergence computed in this study; and, finally, there are regions of uncertainty where no model is consisten tly superior, so forecasts over these regions should be treated with c aution.