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As a result of taking instantaneous cape and capes at discrete time steps the EFI can exhibit a stripy structure in the case of fast moving squall lines or very convective fronts as in the example in Fig. 2. This is an issue because the cold front is not jumping in reality, but is moving continuously from west to east. Replacing cape and capes with mxcape6 and mxcapes6 removes the stripy behaviour and provides a smoother and more realistic forecast field due to better sampling. Smaller scale discretization apparent on the top centre panel for HRES (attributable to the use of values at 1h intervals) is not manifested on the EFI because it will effectively be smoothed out by frontal-timing spread within the ensemble.
Fig. 2. The EFI (and SOT) for CAPE-shear as well as the CAPE-shear high-resolution forecast in for a case of a fast moving cold front. Stripy fields of instantaneous CAPE-shear and the EFI is EFI/SOT (see black lines) are 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 provides information on how different are the cumulative distribution functions (CDFs) of the ensemble forecast and the model climate are. Therefore, 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 convection is convective hazards are 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 the model climate and the ensemble forecast CDFs. Now with replacing cape with 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.
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