Upper ridge will be present across the British Isles on Thursday, with associated dry mid/upper levels and subsidence providing a capping inversion around 600mb. Residual moisture will exist at low-levels across western Britain which, combined with diurnal heating and orographic forcing / low-level convergence will be sufficient to create isolated heavy showers, particularly over higher terrain. Given limited convective depth (and hence relatively warm ELTs), lightning seems rather unlikely, or at least will be fairly isolated if it does occur.

Geopotential heights will fall relatively quickly on Thursday night as sharp Atlantic upper trough approaches from the southwest - enabling some convective activity (with limited depth) to continue to migrate eastwards across Midlands/northern England overnight into the early hours of Friday. Again, lightning seems unlikely / isolated with this. 

Scope also for some mid-level convection to develop over the western English Channel towards Friday morning (end of this forecast period) in the vicinity of Start Bay / Lyme Bay and Channel Islands - have omitted introduction of a LOW threat area here due to uncertainty.