Day 1 Convective Outlook: Sun 28 May 2017
VALID 06:00 UTC Sun 28 May 2017 - 05:59 UTC Mon 29 May 2017
ISSUED 14:33 UTC Sun 28 May 2017
ISSUED BY: Chris/Dan
*Update at 1430z on Sunday to shift the main empahsis 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.