In summer 2015 ECMWF introduced, in test mode, two new EFI parameters for forecasting severe convection - for CAPE and for CAPESHEAR CAPE-shear - that are described below. The test period is now over, and accordingly the parameters are now included in the ECMWF real-time catalogue (see here) and are available in dissemination. In the catalogue the EFIs for CAPE and CAPESHEAR CAPE-shear have the short names of "CAPEI" and "CAPESI" respectively. Charts based on these parameters continue to be available on the ECMWF web-site (here).
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While a global NWP model cannot be expected to forecast individual convective cells, such a model can tell the user whether the broadscale environment is favourable for development of deep moist convection (DMC). Based on this premise, and following user requests and extensive testing, the new EFI parameters were added to assist with the forecasting of severe convection: the EFI for CAPE and the EFI for CAPESHEAR CAPE-shear (=CSP, for "CAPE-SHEAR hear Parameter").
- CAPE combines the effects of two of the necessary ingredients for DMC: instability and moisture. The higher the CAPE the more unstable the air mass is.
- CSP is computed according to:
where deep-layer wind shear
is computed between levels l1=925 hPa and l2=500 hPa, and the second term is proportional to the maximum vertical velocity in convective updraughts as computed using simple parcel theory, i.e.:
. CSP is targeted at forecasting organised DMC, such as supercell convection, as the deep-layer wind shear helps to organise convection into long-lived cells. CSP units are m2/s2 .
Practical remarks
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Further details and practical information about the EFI for CAPE and CSP are also available in the help section below the EFI web charts, in the sub-section entitled "EFI for CAPE and CAPESHEARCAPE-shear" here: real-time EFI-related products (select the CAPE or CAPESHEAR CAPE-shear chart, then page down to see/open this subsection).
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