Convective Outlook: Sun 28 May 2017
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sun 28 May 2017 - 05:59 UTC Mon 29 May 2017

ISSUED 20:20 UTC Sun 28 May 2017

ISSUED BY: Chris/Dan

UPDATE 2020 UTC Latest observational analysis depicts expanding MCS over northern France, this captured reasonably well by some model guidance and expected to be advected NE-wards into S/SE England and parts of East Anglia, though weakening with time late in the night. MDT therefore expanded eastwards to cater for this forecast evolution.

Further pulses of elevated convection are likely on the western periphery of destabilising plume from Lyme Bay across the Midlands to Lincolnshire, but given more marginal instability here it is questionable how widespread lightning activity will be, hence a downgrade to SLGT for now.

UPDATE 1445 UTC Main emphasis shifted a little further west due to model trends

Upper trough approaching Iberia will advect a plume of high ThetaW air northwards across southern Britain through the course of Sunday evening and overnight into Monday. Destabilisation of this plume is expected, with upper forcing combining with isentropic upglide to allow areas of elevated thunderstorms to develop and expand in coverage - at least for a time - before general weakening/reducing trend is anticipated later in the night. 

Current thinking is activity will develop around the 19-22z timeframe over the English Channel / Channel Islands / SW England, growing upscale as the whole area of potential shifts NE-wards through the night. Steep mid-level lapse rates and reasonable CAPE suggests lightning will be notably frequent with any thunderstorms, especially farther east where such parameters will be more favourable.

As is often the case in such situations, there is some uncertainty as to the exact forecast evolution and position of areas most likely to experience thunderstorms - as such, the exact position of the SLGT/MDT is subject to some alterations. Some hail and strong gusts of wind will be possible with some of this convective activity.