A messy situation is expected on Thursday with various areas of dynamic and convective precipitation running northeastwards across England and Wales, with more widespread destabilisation of the warm, moist airmass taking place as the Atlantic trough approaches. A broad SLGT has been issued, but it is worth noting there is some uncertainty as to how active (lightning-wise) some of this convection will be, and it is quite likely some areas will remain lightning-free - but given the uncertainty it is impossible to be any more precise as to the areas most likely to be affected. The main threat will be the risk of local flash flooding given high moisture content.

If sufficient insolation can develop (which is questionable given the rather extensive cloud cover) to break the quite significant capping inversion, there may be scope to develop surface-based thunderstorms. Strong instability is signalled towards the SE, but here the cap is much stronger, whilst forcing is much stronger to the NW, so a middle-ground approach somewhere across the S Mids then running NE-wards to Lincs / E Anglia seems the most likely area should any activity become rooted in the boundary layer. Given the environmental conditions, these thunderstorms could be severe, perhaps even supercellular, with large hail up to 3.5-4.0cm in diameter, and perhaps a tornado (along with the associated risk of flash flooding also). This scenario is given a low probability at the moment, but we have issued a SVR to highlight the areas that may be affected should an overlap of ideal conditions occur.

This risk will also be limited by further contamination of medium-level instability spreading NE-wards from Biscay/Brest peninsula, which will likely occur in various waves through the day and more especially once again on Thursday night.

Across Scotland and Ireland / Northern Ireland, the approaching Atlantic upper trough and associated cool mid-levels, atop warm SSTs and diurnally-heated land, will allow a few scattered showers and thunderstorms to form - especially so across W-C Ireland into W Northern Ireland where a SLGT has been issued. Hail up to 1.0cm in diameter will be possible with this activity, perhaps even here some marginal supercellular characteristics given strong DLS and slight backing of the surface winds.