Taking account of previous ECMWF ENS solutions - Lagged Ensembles

An ensemble of NWP model runs starting from different data times is known as a lagged ensemble.   Combining the current and recent ensembles into a larger ensemble (as in Fig6.1.1.2-1) 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. 


Fig6.1.1.2-1:  Schematic illustration of the relation between the latest ensemble (blue lines) and two previous ensembles (green  and red lines)