Convective Outlook
VALID 06:00 UTC Mon 30 May 2022 - 05:59 UTC Tue 31 May 2022
ISSUED 06:52 UTC Mon 30 May 2022
ISSUED BY: Dan
An elongated upper low covers the British Isles on Monday, centred primarily over Scotland. This will create an unstable environment, especially in response to diurnal heating inland yielding 200-400 J/kg CAPE. Showers/longer spells of rain will already be affecting northern portions of both Britain and Ireland first thing Monday morning, and these will likely turn more convective through the day, with numerous other showers developing elsewhere. Showers will, in places, become focussed along more organised low-level convergence zones, such as SW England - M4 - East Anglia; but even the location of these zones will probably shift slowly eastwards with time. Nonetheless, the relatively slow movement and shower training could give some locally high rainfall totals and the risk of some local surface water flooding.
As was the case on Sunday, convection will be generally restricted to below 14,000ft and this will limit the lightning potential, however a few cells could potentially punch as high as 18,000ft and be capable of producing a few sporadic lightning strikes for a time. This appears to be most likely in a zone from Wiltshire to East Anglia/The Wash where low-level convergence will aid forced ascent, and across central/northern Scotland where a combination of orographic forcing and onshore breeze convergence aids lift. Shear will be weak across northern Britain under the main upper low, leading to pulse mode, but slightly stronger flow along the southern periphery of the upper low, in conjunction with some backing of the low-level winds, will increase both speed and directional shear across the Midlands / East Anglia / southern England, and this may also help tip the balance in favour of a few lightning strikes. Confidence on coverage of lightning, and exactly where, is not particularly high but have tentatively introduced a very marginal SLGT. The strongest cells could produce hail and gusty winds 30-40mph. The slack pressure pattern and areas of low-level convergence will also be favourable for a few funnel clouds. Unlike Sunday evening, the presence of the upper low and associated shortwaves rotating around will maintain showers right the way through Monday night, albeit with a lower (but non-zero) risk of lightning.
