Convective Outlook: Thu 05 Aug 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Thu 05 Aug 2021 - 05:59 UTC Fri 06 Aug 2021

ISSUED 07:12 UTC Thu 05 Aug 2021

ISSUED BY: Dan

An upper trough will swing across Ireland on Thursday, while becoming increasingly negatively-titled. On the forward side, outbreaks of frontal rain will spread erratically northwards and eastwards, with some convective components likely in places. Behind this, cold mid-levels overspreading diurnal heating inland will yield 400-900 J/kg CAPE across much of Ireland, and it is likely numerous showers and thunderstorms will develop here during the day. Convection could be notably tall, with cloud tops potentially pushing towards 32,000ft. Within the main upper trough, deep layer shear will be limited to 10-15kts resulting in fairly slow storm motion (~10kts) over Connacht and C / N Leinster, but this will likely increase across Munster later in the afternoon as stronger westerly flow aloft approaches, perhaps pushing DLS to 25-30kts with cells moving at a reasonable pace across southern Ireland as a result. Nonetheless, there is scope for localised flooding, especially over Connacht, Leinster and perhaps S Ulster. Hail 1.0-1.5cm in diameter will be possible, perhaps locally larger where any sustained/organised thunderstorms can develop (perhaps this most likely in southern Ireland) - alongside gusty winds. Showers/storms will tend to slowly weaken during the second half of the evening, merging into periods of showery rain in places.

Elsewhere, there is the risk of one or two isolated thunderstorms in west Wales and the West Country later in the afternoon/early evening to the rear of the main frontal rain. Also, as a narrow dry intrusion slides eastwards across England and engages with the front, close to the left exit region of a mid-level jet, there could be some sporadic lightning during the evening hours across the E Midlands and eastern England before the front exits to the North Sea. However, confidence is not particularly high and so for now have refrained from introducing higher risk levels. 

Overnight, the main focus (aside from the North Sea and perhaps E Scotland) will probably be the Irish Sea between E Northern Ireland - NW Wales - Cumbria, including the Isle of Man, where a few isolated lightning strikes may be possible from showers in the area.