VALID 06:00 UTC Wed 16 Aug 2017 - 05:59 UTC Thu 17 Aug 2017
ISSUED 23:12 UTC Tue 15 Aug 2017
ISSUED BY: Dan
Upper ridging will be in place across many parts of the British Isles at the start of Wednesday, but an approaching frontal system associated with a plume of relatively high WBPT airmass will move eastwards, engaged by a couple of shortwaves rotating around the main upper trough.
As a result, there will be potential for some instability release embedded within showery outbreaks of rain, with two main zones of interest; one beginning over SW England and Celtic Sea mid-late afternoon/early evening and then migrating NE-wards across England and Wales during the evening/night hours - confidence is quite low at the moment as to how deep embedded convection will be, and hence how widespread (if any) lightning activity will be. For now, we refrain from upgrading to a SLGT.
Better agreement exists for some deep convection to develop during the afternoon and evening hours (presumably along the cold front), over parts of Republic of Ireland / Northern Ireland then propagating NE-wards towards W/SW Scotland. This activity should benefit from some reasonable DLS; in fact a low-topped supercell cannot be ruled out which may produce an isolated tornado - this more likely over Republic of Ireland / Northern Ireland.