Ensemble forecast

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  • The use of ensemble predictions derived from operational weather forecasting models will identify the expected ‘spread’ of weather conditions and assess the probability of particular weather events. As such, it influences the confidence a forecaster places on weather events taking place.  

    In the European Centre for Medium-term Weather Prediction, the operational model is re-run at a lower resolution (the control run) and this is then repeated 50 times, each with slightly different starting conditions. These ensemble runs are shown in the graph above as the grey lines; the average is shown in yellow.    

    If the single (grey) curves lie closely together, the weather situation is stable and confidence of outcomes is high. If the single ensembles spread over a wider range, confidence is lower; this is usual after more than one week (as shown in the graph over the last few days).  

    The graph also shows the operational runs of the ECMWF model (red) and that of NCEP (the USA GFS model, shown in blue).  If these correspond with the ensemble runs, confidence may be confirmed; if they do not, a more cautious interpretation may be needed. The dark green curve shows the values as they appear in our Meteobase product – this represents a blend of the individual models, including the ensembles, together with fine-tuning by forecasters (the value-added information).

    Please contact us for more information on ensemble forecasting and how this affects the confidence a forecaster places on weather events taking place.


    Latest 15 days ensemble forecast temperature for London

    Image 1: Latest 15 days ensemble forecast temperature for London

    Latest 15 days ensemble forecast wind for London

    Image 2: Latest 15 days ensemble forecast wind for London

    Latest 15 days ensemble forecast cumulated rainfall for London

    Image 3: Latest 15 days ensemble forecast cumulated rainfall for London