VALID 06:00 UTC Wed 07 Nov 2018 - 05:59 UTC Thu 08 Nov 2018
ISSUED 21:48 UTC Tue 06 Nov 2018
ISSUED BY: Dan
Main Atlantic upper low remains to the west of the British Isles during this period, but with a succession of shortwaves / impulses running northeastwards on the forward side to provide episodes of stronger forcing and hence some convective interest.
On Wednesday morning, pulses of showery rain will be affecting SW England and S Wales, with the potential for some isolated to sporadic lightning, especially close to windward coasts. During Wednesday daytime and evening hours, most of the lightning activity will likely be reserved for the English Channel where cold air atop warm SSTs will generate 500-800 J/kg CAPE. Southwesterly steering flow will serve to push these heavy showers into S / SE England for a time during the afternoon / early evening, before ridging aloft results in a gradual decay in shower activity here during Wednesday night. A SLGT has been introduced where there is a reasonable chance for some sporadic lightning activity.
On Wednesday night, a strongly-forced convective band (occlusion on FSXX) will develop and move across Ireland and the Celtic Sea, towards west Wales and SW England during the latter stages of the night. While some guidance suggests a transition to more dynamic precipitation may occur, given the strongly-sheared environment, warm SSTs and abundance of CAPE, some broken line segments seem possible, with sporadic lightning in places. There are subtle differences among NWP as to the timing of this feature, but nonetheless some squally winds would be possible with the most intense cells.