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Description information

Extreme Forecast Index (EFI) is a tool to identify where the EPS forecast distribution differs substantially from that of the model climate. It contains information regarding variability of weather parameters, in location and time and can highlight an abnormality of a weather situation without having to define specific space- and time-dependent thresholds.

The EFI value is computed from the difference between two cumulative distribution function (CDF) curves: one for the M-Climate, and the other for the current ENS (ensemble forecasting) forecast distribution. The calculations are made so that more weight is given to differences in the tails of the distribution (see Figure ).

http://www.extendweather.com/Images/Help/about-efi-3.png

If the forecast probability distribution agrees with the M-climate distribution then EFI = 0. If the probability distribution (mean, spread and asymmetry) does not agree with the climate probability distribution, the EFI takes non-zero values. In the special case where all the members forecast values above the absolute maximum in the M-climate, the EFI = +1; if they all forecast values below the absolute minimum in the M-climate the EFI = -1