Page History

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• Extreme weather indicated by EFI and SOT:
  • has been assessed against IFS model climatology as derived for M-climate, ER-M-climate or S-M-climate and these can differ from observed climatology.

  • does not necessarily indicate high impact as:

    • Rainfall has varying significance according to location (e.g. 2mm rainfall in the desert might be very unusual but have little physical impact).

    • Windstorm impact can depend on whether trees are in leaf, whether ground is saturated, stability of buildings, etc.

    • Past history is important but is not directly accounted for (e.g. the impact of a heavy rain event on saturated ground is greater than if the ground can absorb the water).

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Although a high EFI value indicates that an extreme event is more likely than usual, the values do not represent probabilities.  Any forecasts or warnings must be based on a careful study of probabilistic information derived from ensemble forecasts.  Examples are meteograms and plumes in addition to the EFI.   Users should note:

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In a few cases there could be an apparent discrepancy between EFI values as indicated by the ecChart probe tool and the CDF curve for the same selected location.  This is because the EFI and CDF may use different but nearby grid points.  The discrepancy, however, is rarely significant.

The M-climate on the CDF plot should only be considered as a reference so is not suitable for accurate calculations of EFI and SOT.  The M-climate is lead-time dependent and there might be differences for different lead-times, especially in the tails of the CDF Plotplot.