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The EFI is a climate-related product which provides information on how different are the cumulative distribution functions (CDFs) of the ensemble forecast and the model climate. So an anomalous forecast does not necessarily translate into a high-impact one. In case of convection this means that an anomalous values of CAPE does not necessarily suggest that convective hazards are likely. For example, climatological values of CAPE in the cold season over the Arctic are so low that severe convective hazards are impossible even if the forecast shows up extreme CAPE. To filter out anomalous but insignificant signals in the EFI, CAPE values less than 10 J.kg-1 are set to 0 before computing both the model climate and the ensemble forecast CDFs. With cape replaced by mxcape6 and capes with mxcapes6, CAPE over 10 J.kg-1 will happen more often and therefore this may show up on the EFI (Fig. 3). To correctly interpret the EFI one should always account for the model climate as well.
Fig. 3. EFI/SOT for CAPE and max CAPE* in Siberia, illustrating that the latter may show up a bit more often.
Finally, as a result of this change, the model climate also changes slightly across the world (Fig. 4a). In the example in Fig. 4b the EFI suggests a bit more extreme CAPE values over NW Spain. The CDFs for a representative location there show what this signal corresponds to in terms of model climate and ensemble forecast distributions.
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b)
Fig. 4 a) Model climate 99th percentile for cape and mxcape6* valid for the end of April and b) an example of the EFI for cape and mxcape* and CDFs of corresponding model climate and real-time ensemble forecasts.
* We refer here to max CAPE (or mxcape6) and max CAPE-shear (or mxcapes6) for distinguishing the EFI of these from current ones but in fact the former will literally replace the latter. Therefore the users will not see any change in the naming and there will not be any additional EFI/SOT, instead the EFI and SOT for CAPE and CAPE-shear will use mxcape6 and mxcapes6.