There are reasonable signs for an area of elevated convection to be drifting across S / SE England at the beginning of this forecast period, continuing to move NW-wards through Saturday morning. Questionable as to how much lightning there will be with this activity given weakening instability, though forecast profiles do suggest some reasonable shear to help with some organisation. Either way, whatever activity there is will likely weaken with time as it continues to migrate across the Midlands and into Wales.

A secondary pulse of elevated convection may develop and move NW-wards across SW England late morning into the afternoon, which would have a better chance of producing lightning - but this is a weaker signal amongst model guidance.

This then leaves a window of opportunity during the afternoon for surface-based thunderstorms to occur. However, the atmosphere will be largely capped by a warm nose at 850-900mb, and so despite increasing instability it is possible very little will actually develop. Greatest potential perhaps across Dorset, Somerset and Gloucestershire, but this very much dependent on enough surface heating to break the cap, which is uncertain due to the potential for extensive mid/upper level cloud associated with earlier elevated convection. Should an isolated thunderstorm develop, it may be severe, capable of producing hail up to 2.0cm in diameter and localised surface water flooding.

The potential for thunderstorms then increases during Saturday evening and night, with numerous elevated thunderstorms likely to develop over the English Channel containing frequent lightning and perhaps some hail. The vast majority of model guidance would suggest thunderstorms will move to the NW, putting SW England and the West Country at greatest risk, broadly Isle of Wight westwards. However, ECMWF has been very consistent over several runs (now joined by 12z EURO4) to produce a much more bifurcated flow, which would then take a very active cluster of thunderstorms NE-wards over Hampshire, Sussex and towards the London area by the early hours of Sunday.

Given the large spread of possible areas affected, it is difficult to pin down a MDT area with any significant confidence - though worth stressing the ECMWF (and EURO4) tends to have a good handle of elevated convection, and its consistent signal over multiple runs is somewhat reassuring. As a result, have followed these trends for the MDT - though if other models are correct, this may need shifting westwards to cover more of Devon and Cornwall.