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Ensemble forecasting

Ensemble forecasts quantify uncertainties in weather prediction and estimate risks of particular weather events.

An ensemble forecasting system samples the uncertainty inherent in weather prediction to provide more information about possible future weather conditions. Rather than producing a single forecast, multiple forecasts are produced by making small alterations either to the starting conditions or to the forecast model itself, or both.

Ensemble forecast systems are designed so that each member should be equally likely, so that the ensemble can be used to forecast the  probabilities of different possible outcomes. Where all the forecasts in an ensemble are similar we can be more confident in the forecast; where they differ we must take more account of uncertainty.

Two ensemble forecasting systems are used at the Met Office: the Met Office Global and Regional Ensemble Prediction Systems (MOGREPS) is used for short-range prediction, while the ECMWF ensemble prediction system is used for the medium range (up to 15 days ahead).

Key aims

  • To develop ensemble prediction systems, improving the representation of uncertainties in both the initial conditions and the forecast models.

  • To continue to develop a range of probabilistic forecast products, particularly to improve forecasts of the risk of high-impact weather events.

  • To support customers in using uncertainty information to manage weather-related risks effectively.

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