VALID 06:00 UTC Sun 30 Apr 2023 - 05:59 UTC Mon 01 May 2023

ISSUED 07:02 UTC Sun 30 Apr 2023

ISSUED BY: Dan

A pronounced upper trough will crest the western Europe upper ridge as it slides eastwards across the British Isles on Sunday. A moist low-level airmass will persist across most areas, with the exception of central and northern Scotland, with dewpoints typically 10-12C. Ireland/Northern Ireland will have the benefit of early occlusion debris clearing eastwards leading to better insolation and surface heating, coupled with being under the upper trough (and associated cold pool) during peak heating hours. As such, an unstable environment is anticipated here, yielding generally 500-1,000 J/kg MLCAPE and resulting in numerous heavy showers and thunderstorms developing through the day, especially in Ulster and Leinster aided in places by orographic forcing and some areas of low-level wind convergence as a surface trough develops through the afternoon. Modified forecast soundings reveal fairly unidirectional winds with height leading to rather weak cloud layer shear (typically 20kts), but potential for cloud tops to reach around 30,000ft (ELTs around -50C). As such, some fairly active thunderstorms will be possible, perhaps more especially in the north and east of Northern Ireland. Cells initially will probably be steered towards the east or northeast on the forward side of the upper trough, but as the trough departs towards Britain during the evening the steering flow may take cells more to the southeast later in the day and through the evening. While shear may not be particularly strong, some fairly robust updrafts in the most organised cells could produce hail up to 1.5cm in diameter (sub-severe). Thunderstorms may spread into or develop over portions of southern Scotland later in the afternoon and into the evening hours.