Convective Outlook: Thu 30 Sep 2021

LOW SLGT MDT HIGH SVR

What do these risk levels mean?

Convective Outlook

VALID 06:00 UTC Thu 30 Sep 2021 - 05:59 UTC Fri 01 Oct 2021

ISSUED 06:59 UTC Thu 30 Sep 2021

ISSUED BY: Dan

A series of frontal systems will cross Ireland and the UK from the west during Thursday and Thursday night. For the most part, the lightning risk is very low / negligible with pockets of limited medium-level instability. Some deeper convection could develop over Ulster and western Scotland during the afternoon, however the main focus is during the evening and night hours as an extending and increasingly negatively-tilted upper trough approaches from the Atlantic, engaging with a second frontal system. Cold air aloft overspreading warm SSTs coupled with increasing PVA/divergence on the forward side of the upper trough could result in more substantial deep convection developing close to a deepening low centre to the north of Ireland / west of Scotland. As such, there could be a few lightning strikes during the evening/night hours across parts of Ireland and towards western Scotland, and later in the night over the Irish Sea towards western coasts of England and Wales. However, confidence on much in the way of lightning, and specific regions, is too low to warrant a SLGT at this stage (one area of consideration is Cumbria/Lancashire/SW Scotland). Gusty winds and hail will be possible in places, and shear may be sufficient for one or two isolated tornadoes, and some transient supercell structures - especially close to the surface low centre where low-level winds will be backed the most. Across England and Wales, increasing convergence along the cold front during the overnight period (although not on the scale of Sunday night/Monday morning) will encourage some line convection to develop, particularly across Wales and the Midlands.