The close vicinity of the longwave upper trough will result in marked cooling in the mid-levels, atop reasonably warm/moist low-level airmass (2m temperatures in the high teens with mid-teens dewpoints). Diurnal heating will lead to increasing instability over Ireland, yielding up to 1,000 J/kg CAPE. This will build in an environment with at least 30-40kts bulk shear, arguably some of the best CAPE/shear overlap experienced so far this year. Ireland will be placed beneath the left exit of the strong jet aloft, creating broad divergence/lift. A cold front will slide erratically northeastwards across Ireland through the day, but it is unclear how widespread any frontal rain may be with this feature - with potential for a wave or closed low to develop along the front and push a more widespread area of rain northwards during the afternoon. Either way, there is scope for deep convection to develop in places, bringing the risk of some scattered thunderstorms. The strongly-sheared profiles and magnitude of CAPE suggests that convection may become organised into line segments, and possibly some supercells. These may be capable of producing marginally-severe hail, up to 2-3cm in diameter, and strong gusts of wind. Fairly low cloud bases, some backing of the low-level winds and 30-40kts 0-1km shear suggests potential for isolated tornadoes.

During the evening hours, the approaching sharp trough will be associated with an impressively strong low-level jet (LLJ). Strongly-forced deep convection is likely to evolve in the vicinity of the cold front, affecting S / SE Ireland, the Irish Sea into SW England, W Wales, and perhaps also the Isle of Man and SW Scotland. Consequently, an increase in lightning activity is likely during the evening hours across Celtic Sea / Irish Sea and adjacent landmasses, and this convection brings the threat of damaging gusts of wind 60-70mph (locally 80mph), and perhaps a few isolated tornadoes too. Further waves of deep convection could evolve overnight behind the cold front, ahead/near another small low pressure centre approaching SW Ireland during the early hours. A SVR has been introduced for the threat of locally damaging gusts of wind and isolated tornadoes, and to a lesser-extent for marginally-severe hail.

Elsewhere, a plume of high Theta-W will linger across much of the near Continent to the southern North Sea through this forecast period, in close proximity to coastal parts of East Anglia and SE England. It is possible some elevated shower/thunderstorm activity could develop in this area at times, more especially on Thursday evening as the aforementioned trough axis swings through and engages this plume. The risk appears greater offshore over the North Sea, but worth monitoring.