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Fig. 2. The EFI for CAPE-shear as well as CAPE-shear high-resolution forecast in a case of a fast moving cold front. Stripy fields of instantaneous CAPE -shear and the EFI is due to taking instantaneous CAPE-shear values at discrete time steps. The EFI forecast looks smoother when using the smoother fields of maximum CAPE-shear in 6-hour periods. The sequence of Air mass RGB imagery shows snapshots of the cold front approaching the south-western parts of the Iberian Peninsular.
The EFI is a climate-related product which means that it shows how cumulative distribution functions (CDFs) of the ensemble forecast compare with the model climate. Therefore, an anomalous forecast does not necessarily translate into a high-impact one. In case of convection this means that anomalous values of CAPE does not necessarily suggest that convective hazards are likely. For example climatological values of CAPE in winter over the Arctic are so low that severe convection is impossible even if the forecast shows up extreme CAPE. To filter out anomalous but insignificant signals in the EFI, currently CAPE values less than 10 J.kg-1 are set to 0 before computing both model climate and ensemble forecast CDFs. Now with replacing cape with mxcape6 and capes with mxcapes6, CAPE over 10 J.kg-1 will happen more often and therefore this will show up on the EFI. To correctly interpret the EFI one should account for the model climate as well.
Finally, as a result of this change, the model climate also slightly changes globally (Fig. 4a). In the example below on Fig. 2b the EFI suggests a bit more extreme CAPE values over
over NW Spain. The corresponding CDFs 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 for cape and mxcape and CDFs of corresponding model climate and real-time ensemble forecasts.