Convective Outlook: Sat 06 May 2023
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sat 06 May 2023 - 05:59 UTC Sun 07 May 2023

ISSUED 06:33 UTC Sat 06 May 2023

ISSUED BY: Dan

Omega block persists across Scandinavia on Saturday placing the British Isles under the influence of an upper trough, albeit the main axis lifting northwards through the day with heights rising from the south with time. A rather messy pattern is anticipated with several low-end SLGTs introduced, most shower activity linked to shortwaves rounding the base of the longwave upper trough in conjunction with surface heating of a moist low-level airmass (Td typically 10-13C) yielding a few hundred J/kg MLCAPE, and orographic forcing/low-level convergence. One shortwave over S/SW Scotland at 06z will lift northwestwards to overlap favourably with peak heating across the NW Highlands, and it is likely several heavy showers and perhaps a couple of weak thunderstorms may develop here. Additional heavy showers may also develop through the day in S/SW Scotland across to the Borders and southwards into the northern Pennines/Lake District, perhaps with a few isolated lightning strikes. With showers training over the same area (or at least nearby), there is the risk of some local surface water flooding here.

Over Ireland, a shortwave will approach Munster mid/late morning and swing northeastwards through the afternoon, again overlapping favourably with diurnal heating and providing the focus for scattered heavy showers and a few thunderstorms to develop. This is likely to be the most favourable environment for a couple of slightly stronger thunderstorms out of the whole of the British Isles on Saturday, with a better overlap of CAPE and modest 20-30kt DLS (especially across Leinster and Ulster where low-level winds will be backed). The strongest cells may produce hail <1cm in diameter and/or wind gusts to 30mph. The aforementioned shortwave will also graze parts of Wales/SW England and could aid a few heavy showers here also (e.g. Devon/Somerset), depending on the degree of surface heating to the west the main surface low/precipitation shield - due to lower confidence here have refrained from introducing a SLGT. Incidentally, any thinning of cloud and modest surface heating could trigger a few heavy showers across other parts of England in advance of and behind the main area of frontal rain (hence the very broad LOW threat area).

During the late afternoon and into the evening hours, a few heavy showers and couple of thunderstorms could affect parts of the English Channel and adjacent Channel Islands/far SE Kent coast.