VALID 06:00 UTC Mon 24 Apr 2023 - 05:59 UTC Tue 25 Apr 2023

ISSUED 06:11 UTC Mon 24 Apr 2023

ISSUED BY: Dan

Within the base of a broad longwave upper trough sat over the British Isles, a shortwave trough will swing southeastwards from Ireland across Wales and southern England during Monday. Beneath and on the forward side of the trough an area of showery rain is expected to drift southeastwards across Ireland, Wales and into southern England. Ahead of this, diurnal heating will lead to steep low-level lapse rates, and could potentially yield several hundred J/kg CAPE as air aloft continues to cool in advance of the trough, depending on how much sunshine persists before cloud and showery rain advances from the north/northwest. Assuming sufficient heating, a sea breeze convergence is likely to evolve along southern counties of England, and perhaps also south Wales, aiding development of heavy showers and possibly a few thunderstorms. A rather messy evolution is likely through the afternoon as showers tend to morph into larger areas of showery rain, however assuming low-level convergence zones persist in the rather slack pressure pattern, perhaps enhanced by outflow at times, then sufficient forcing may be present for additional sporadic bursts of lightning almost anywhere across southern England, before eventually weakening/reducing through the evening. Main caveat is how far inland the sea breeze convergence may push, which will depend on the amount of sunshine/surface heating in the morning/early afternoon and will ultimately determine to some extent how far north to extend the SLGT - it is plausible it may need to be trimmed closer towards the south coast, reducing the aerial extent for example. This is a rather conditional outlook, and requires sufficient surface heating and convergence in order to obtain deep convection and a better chance of some lightning occurring.