On the prediction of forecast skill.

Using 10- day forecast 500 mb height data from the last 7 year, the potential to predict the skill of numerical weather forecasts is discussed. Four possible predictor sets are described. In discussing the physical mechanisms that underlie the use of these predictors, three important components of forecast skill variability are discussed; the quality of the initial analysis, the intrinsic instability of the flow, and the role of model systematic errors.