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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 the case of convection this means that an anomalous values of CAPE does do 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.
a)
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/SOT for cape and mxcape* and CDFs of corresponding model climate and real-time ensemble forecasts.
*Naming Conventions: We refer on this web page to "max CAPE" (or mxcape6) and "max CAPE-shear" (or mxcapes6) for distinguishing the EFI/SOT of these in cycles from 47r1, from the equivalent EFI/SOT fields used up to and including cycle 46r1, but in fact when the model changes the former literally replaces the latter. Therefore users do not see any change in the naming - e.g. in ecCharts - and there will not be any additional EFI/SOT; instead the EFI and SOT for CAPE and CAPE-shear will continue to exist but they will use instead mxcape6 and mxcapes6.