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In the case illustrated (Fig8Figs8.1.9.6-21 ) there is a dipole structure in & 22) the structure of the convective EFIs patterns differs. These are:
- extreme CAPE (for the season) across southern Ireland to northern England.
- extreme CAPE-shear (for the season) across Celtic Sea towards Wales. In this example CAPE-shear is dominated by the extreme wind shear.
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Fig8.1.9.6-23:Forecast wind hodograph relative to storm movement. Curved forecast hodographs in the lowest 3 km give high helicity relative to the storm - even in the lowest 500 m. This is one of the predictors for tornadoes.
Example 3:
A major outbreak of severe convection occurred on 26 May and CAPE-shear EFI covers the wide area of severe convection. Within the CAPE shear areas 43 tornadoes and hail very large hail (over 50mm diameter) occurred mainly in the west of the area and severe convective gusts were reported mainly in the east. Tornadoes and very large hail usually occur in the presence of supercells. The CAPE-shear EFI signal was much stronger than that of CAPE EFI. This gives information about the environment – large instability but also presence of strong deep-layer wind shear. In such kind of environment well-organised convection tends to develop if enough lift is provided.
Fig8.1.9.6-24: Observed severe weather over USA 26 May 2024 (left diagrams). EFI forecast of CAPE and CAPE-shear DT 00UTC 24 May 2024, VT 00UTC 26 May to 00UTC 27 May 2024 (right diagrams). The CAPE-shear EFI signal is much stronger than that of CAPE EFI which illustrates the importance of strong instability together with significant shear when forecasting severe convective weather.
Considerations when forecasting Mesoscale Convective Systems (MCS) and Supercells
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