Taking account of solutions from ECMWF and other models - Grand Ensembles

An ensemble of NWP model runs using different models but starting from the same data times is known as a grand ensemble.  Combining the current ensembles from different models into a larger ensemble (as in Fig6.1.1.1-1) can show possible consistency in forecasts and identify any different evolution.

It is inappropriate to rely on the results of any individual ensemble member or ensemble run itself.  But if there is some indication of extreme or hazardous weather the threat should be passed on to users, but with a very low probability.  Nevertheless, there can be some agreement between the spread and jumpiness. 


Fig6.1.1.1-1: Schematic illustration of the relation between the latest ENS (green lines), the three latest CTRL (or HRES) (red lines), and results from other forecast models (blue lines).  Here the three latest CTRL (or HRES) solutions are in agreement with ENS solution but two other forecast models show some more extreme troughs or higher maxima.