Taking Acount of previous ENS solutions - Grand or Lagged Ensembles
Occasions when there is a clear divergence between the latest and previous developments in the ensemble or ensemble mean occur increasingly rarely - but if it does the forecasters is in a difficult position. Nevertheless, there can be some agreement between the spread and jumpiness.
Fig6.3.4B: Schematic illustration of the relation between the latest ensemble (blue lines) and two previous ensembles (green and red lines)
An ensemble of NWP model runs starting from different data times is known as a lagged ensemble. Forecasters might consider combining the current and recent ensembles into a larger lagged ensemble (as in Fig6.3.4B). 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.
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