members of an ensemble around the mean, in this case summarized by the ensemble spread, can be used to improve forecasts relative to linear regression. Whether or not linear regression can be beaten by using the ensemble spread in this way varies, depending on the forecast system, forecast variable and lead time. Predicting the size of forecast changes In addition to being used to improve predictions of uncertainty, the ensemble spread can also be used as a predictor for the likely size of changes in the mean forecast from one forecast to the next. This works because, in some ensemble forecast systems, narrow ensembles tend to precede small changes in the mean, while wide ensembles tend to precede larger changes in the mean. This has applications in the trading industries, for whom understanding the likely sizes of future forecast changes can be important. Co-ordinated research The Observing System Research and Predictability Experiment (THORPEX) is a 10-year international research and development programme to accelerate improvements in the accuracy of one-day to two-week high impact weather forecasts for the benefit of society, the economy and the environment. It establishes an organizational framework that addresses weather research and forecast problems whose solutions will be accelerated through international collaboration among academic institutions, operational forecast centres and users of forecast products. One of its key components is THORPEX Interactive Grand Global Ensemble (TIGGE), a World Weather Research Programme to accelerate the improvements in the accuracy of 1-day to 2 week high-impact weather forecasts for the benefit of humanity. Centralized archives of ensemble model forecast data, from many international centers, are used to enable extensive data sharing and research. See also Chaos theory Climate ensemble Consensus forecast Ensemble Kalman filter Ensemble (fluid mechanics) Forecasting Probabilistic forecasting THORPEX Interactive Grand Global Ensemble North American Ensemble Forecast System References Further reading External links TIGGE Research Page TIGGE Tropical Cyclone Track data Archive at NCAR THORPEX Research Page Climate and weather statistics Monte Carlo methods Numerical climate and weather models Statistical forecasting