Convective Outlook
VALID 06:00 UTC Sat 22 Oct 2022 - 05:59 UTC Sun 23 Oct 2022
ISSUED 07:44 UTC Sat 22 Oct 2022
ISSUED BY: Dan
Upper ridging will build across western Europe into the British Isles on Saturday. Some showers and showery outbreaks of rain are likely during the daytime in N + E Scotland, N + W Ireland, and then eventually SW England, S Wales and S Ireland. Overall, the lightning risk is relatively low during the day due to a combination of either skinny CAPE, restricted convective depth and/or fairly moist profiles. Convection that approaches SW Britain and S Ireland through the day appears to be a mixture of surface-based and elevated and could produce a few odd lightning strikes. Current thinking is this will eventually grow upscale into a more organised band of rain during the late afternoon and evening hours over the Celtic Sea, S Wales and pushing into S Ireland.
Overnight, the upper ridge will clear eastwards to central Europe as an upper low west of Biscay slowly approaches. Strengthening and backing flow aloft will encourage advection of a ~14C 850hPa Theta-W plume from France into southern Britain, in conjunction with an approaching shortwave running northwards on the eastern flank of the upper low creating forced ascent, will ultimately result in an increasing coverage of convection and therefore potential for thunderstorms. However, given rather deeply moist profiles and forced ascent, this could grow upscale into a larger area of showery rain with embedded heavy bursts of rain, but limited lightning opportunity - so this casts some uncertainty over how much lightning may occur. If cells can remain relatively discrete then there could be a few fairly active storms during the overnight period. Greatest concern may be local surface water flooding from torrential downpours. Towards the end of the night, some suggestions of a substantial dry intrusion in the vicinity of the cold front, on the rear side of any rain, could aid in the development of some active thunderstorms over the likes of Wiltshire, Dorset, Somerset, E Devon and SE Wales, with an associated risk of 50-60mph gusts - but low confidence on this evolution.
