Surface dewpoints of 10C are expected across central and eastern England during the morning, but this will eventually be eroded from the west through the day as drier air advects eastwards with the passage of the cold front. Main upper forcing (and hence steeper lapse rates) will tend to arrive later, arriving over Wales around 11-12z for example, and then migrating NE-wards through the afternoon - hence there is somewhat of a lag between favourable surface conditions not overlapping more favourable mid/upper level conditions. This creates some uncertainty as to whether much deep convection can develop given increasingly dry forecast profiles and somewhat of a warm nose at 700mb.

Some convection-allowing models simulate several showers during the afternoon, from S + E Wales through the Midlands to Yorkshire / Lincolnshire. Given 400-600 J/kg CAPE and 30-50kts DLS, it is certainly possible some lightning activity could occur should any deep convection develop, including hail up to 1.5cm in diameter - however, confidence is not particularly high on whether many showers/storms will actually form. Given lowering dewpoints, any clouds that do form will likely be fairly high-based too. An upgrade to SLGT is possible for some of these regions if confidence improves.

Some showers/thunderstorms may get close to Kent/Sussex from northern France late afternoon into the evening hours, though most activity will likely stay over the nearby Continent. The approach of an upper (and surface) low from the southwest may also increase deep convection potential during the early hours of Wednesday over southern counties of England.

Behind the northward-advancing occlusion, a few heavy showers may develop during the afternoon/early evening over The Midlands northeastwards into SE Northern Ireland. Instability and shear overall are a little weaker here, and cloud cover may be somewhat of an issue, but some lightning is also possible with any stronger cells - and an upgrade to SLGT may also be considered if confidence increases.