Behind this front, increasing insolation over southern England during the afternoon hours may allow surface-based deep convection to occur late afternoon into Thursday evening, given heating of this higher WBPT airmass, surface convergence and the approach of the Biscay upper trough. Question marks remain over the extent of the cloud cover, which may act as an inhibitor - however, the vast majority of NWP guidance still develop some thunderstorms, if rather isolated in some cases. A SLGT has been issued to highlight the areas at risk (primarily Surrey/north Hampshire westwards to Somerset, then north and west from here across SW Midlands to mid-Wales), with perhaps some small hail from the most active cells and a risk of localised flash flooding. Additional thunderstorms may also be advected from France / develop in-situ over the Channel towards S/SE England in the evening (hence the SLGT here), but with lower confidence and perhaps weakening as they do so.