Extreme High Swell Events on the Moroccan Atlantic Coast

4.0 Case Study 1 » 4.4 Step 3: Forecasting the Marine Situation » 4.4.4 Extreme Forecast Index (EFI)

We’ve looked at both model forecasts. Now we’ll use the Extreme Forecast Index or EFI to evaluate the ECMWF forecasts.

EFI is a predictive parameter used to assess the abnormality of a forecast weather situation based on the difference between the ECMWF ensemble prediction system distribution and the ECMWF model’s climatology. The EFI is produced for maximum significant wave height and other parameters.

The EFI uses values from -1 to +1.

  • If all of the ensemble members forecast values are above the model-climate maximum, EFI = +1
  • If all the forecast values are below the model-climate minimum, EFI = -1

EFI magnitudes of 0.5 to 0.8 (irrespective of sign) generally signify that "unusual" weather is likely. Magnitudes above 0.8 usually signify that "very unusual" weather is likely.