Convective Outlook: Wed 10 Oct 2018
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 10 Oct 2018 - 05:59 UTC Thu 11 Oct 2018

ISSUED 21:16 UTC Wed 10 Oct 2018


UPDATE 21:16 UTC No changes made to the forecast - latest guidance continues to suggest some notable instability (500-800 J/kg CAPE) developing over the English Channel as the shortwave briefly intensifies, between 02z - 06z. This would be the main timeframe for any lightning activity, but the risk is broad - stretching from E Devon to East Sussex, then points north from there into Thursday morning. Vast majority of model guidance remains capped with little to no precipitation forecast to develop over the area of interest during this timeframe - and so no SLGT has been issued at this juncture

Upper low over northern Iberia (the remnants of the rainfall event over southern Britain last Saturday) will weaken and be absorbed into the forward side of the main upper trough approaching from the Atlantic. An increasingly moist airmass will advect from France across southern Britain during Wednesday evening and night, destabilising as subtle upper forcing engages with the moisture plume. 

Sporadic bursts of showery rain will likely develop over the English Channel and portions of England and Wales during Wednesday evening and overnight into Thursday morning. A few hundred J/kg CAPE accompanied with subtle forcing may allow some sporadic lightning to occur, moreso on the rear (western) side of any showery rain, but unlikely to be too widespread. 

Naturally there is some uncertainty as to where any lightning may occur - but two main areas of interest might be E Devon / Dorset / Somerset / Wiltshire into SE Wales during the night, then another area towards SE England / Home Counties by Thursday morning at the end of the forecast period. However, neither look convincing enough to warrant an upgrade at this stage.