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Forecaster intervention with the ENS

It is often taken for granted that forecasters cannot improve on the ENS.  But forecasters can manually intervene by using their experience for a certain location.  They can be guided by verification of previous events to correct tendencies of the ENS to over- or under-forecast probabilities.  These modifications are often appropriate at coastal locations or in mountainous regions.  This is because local effects may be significant and/or the grid point nearest to the location that is used for the meteogram may not be typical nor appropriate. 

Taking account of other state-of-the-art NWP models - Grand and Lagged Ensembles

Ensemble forecasts give the most consistent guidance.  But one should not rely on any individual result.

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Forecasters may have to assess the probability of an event by balancing probability information from each of several sources.  It is not unusual to have to balance information such as.  This might be an event is forecast by:

• a 50% probability from the ENSensemble.
• a 30% probability from a different, but equally reliable, statistical or ensemble system.
• five of the last six ensemble control forecast and/or other state-of-art models have forecast the event.

Forecasters should treat forecasts from different NWP models as part of a “multi-model ensemble”.  This has an advantage because the members differ slightly from IFS in their initial conditions and model characteristics.  Note, on average:    

• the "best" NWP model of any kind is not necessarily the best on a particular day.
• an NWP model that has recently performed significantly better or worse than other models (of about the same average skill) is not likely to continue to do so.

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