A few isolated to well-scattered showers or thunderstorms may form this afternoon over high ground of Northern England and Scotland. However, the majority of activity will begin this evening and persist overnight, as outlined below...

Shortwave trough is likely to engage with instability axis as it crosses NW Ireland / Northern Ireland on Tuesday afternoon/evening, with an environment with Tds in the high teens Celsius, yielding 1,000-2,000 Jkg^-1 MLCAPE. Scattered thunderstorms are expected to erupt late afternoon through the evening hours, drifting to the N/NE. Given high CAPE, 30-40kts DLS and backed surface winds, any discrete storms may become supercells, at least for a time, with an associated risk of hail to 3.5cm in diameter, strong, gusty winds and perhaps a tornado - SVR issued to cover all three threats. Some parts of C and W Scotland may require an upgrade to MDT for activity expected this evening/tonight - trends will be monitored.

Elsewhere, falling heights in advance of the upper trough will lead to destabilisation during late Tuesday evening and through early hours of Wednesday, with scattered thunderstorm development occurring during the evening hours, these moving NE-wards through the night while expanding in coverage - MDT issued where risk of thunderstorms is considered higher, but as is often the case in such situations, this area may need to be modified in placement/size as convective trends become more clear nearer the event.

Given nocturnal cooling will have occurred to a certain extent before any significant convection develops, most cells will be elevated but still pose a risk of local flash flooding from heavy downpours and elements of backbuilding, and also a hail threat - SVR then issued to cover the greatest risk of flooding / large hail. Significant CAPE and steep lapse rates suggests lightning could be quite prolific in places.