Several episodes of thunderstorms are possible during this forecast period - in general, for England / Wales the risk of lightning is mainly across the southern half of the SLGT during Thursday daytime, the focus then shifting to the northern half of the SLGT on Thursday night / early Friday. Main focus for Northern Ireland / Republic of Ireland will be Thursday afternoon and early evening.

Elevated convection will likely be ongoing at the start of this forecast period, associated with destabilisation of relatively high WBPT plume, over southern England / south Midlands, moving westwards into S Wales and parts of SW England. Some sporadic lightning continues to be possible with this activity, although instability reduces as storms continue to drift to the west, so probably with a weakening trend as they move into Wales / SW England.

By the afternoon, there is fairly good model agreement for any thunderstorm potential to become primarily focussed along the moisture plume, in a SE-NW corridor from Cen S England to S Wales. By this point, rain will be evolving into a messy mix of dynamic and embedded convection elements, though should any thunderstorms develop along this zone then they will quite likely be elevated - however, there is scope for some to become rooted in the boundary layer if enough surface heating can occur, either along or to the north of this frontal boundary. Some high-resolution model guidance suggests the potential for a couple of surface-based thunderstorms during the second half of the afternoon near or just north of the M4, drifting west into E / SE Wales towards evening. This area therefore has the potential to be upgraded to MDT; should thunderstorms develop here lightning could be quite frequent, accompanied by hail and gusty winds.

Main threats will be surface water flooding from prolonged heavy rain running over similar areas, particularly Cen S England and along the M4 corridor into the SW Midlands. Depending on developments, the SLGT may also need extending into parts of Devon and Cornwall.

Remnants of mid-level convection / instability (from Wales) will drift westwards into southern and eastern Ireland on Thursday morning - this airmass then destabilising further in response to surface heating, yielding 500-900 J/kg CAPE. Low-level convergence will aid in the development of a few scattered surface-based showers and thunderstorms along a N-S line, starting on the eastern side of the SLGT mid-afternoon and drifting slowly to the west into the early evening, before decaying as nocturnal cooling of the boundary layer commences.

Shear is not particularly strong, and so most showers/storms will tend to be of the pulse variety, an individual cell lasting less than an hour etc. This is also somewhat dependent on how much cloud will spill from the east, reducing surface heating. An isolated heavy shower / thunderstorm is also possible in western Northern Ireland.

During the second half of the evening, a renewed pulse of high WBPT airmass will advect westwards towards East Anglia / SE England, and then into other portions of eastern England and the Midlands during the early hours, destabilising as a shortwave drifts from BeNeLux to eastern England around the northern periphery of the upper low over NW France. An increase in coverage of elevated showers and thunderstorms is expected with time, drifting WNW-wards across East Anglia - Midlands - southern N England - Wales. This activity will tend to merge into a larger area of heavy rain with embedded lightning as the night progresses, and hence becoming a rather messy mix of dynamic and convective precipitation.

An upgrade to MDT may be required for parts of East Anglia in particular, if confidence on thunderstorm coverage improves - any thunderstorms that develop here will likely produce very frequent lightning given expected instability, with lightning frequency and coverage generally decreasing further west as profiles become saturated and instability reduces.