VALID 06:00 UTC Wed 12 Apr 2023 - 05:59 UTC Thu 13 Apr 2023

ISSUED 05:05 UTC Wed 12 Apr 2023

ISSUED BY: Dan

An exceptionally deep but vertically stacked cyclone will linger close to/across Scotland for most of Wednesday. A strong mid and low-level jet will round its western and southern flank through the day. Several clusters of shower activity are likely as shortwave troughs rotate around the main parent low, one such feature affecting SE England first thing in the morning. The primary focus for lightning activity will likely be with the leading portion of the wrap-around occlusion as it swings from southern Ireland into Wales and southwest England during the morning hours. Strong forcing for ascent on the forward side of the, initially positively-tilted, upper trough in conjunction with relatively warm SSTs yielding several hundred J/kg CAPE may allow some rather active embedded thunderstorms to occur for a time, but gradually through the day as the upper trough swings northeast to become negatively-tilted, a weakening trend in lightning activity may occur with eastward extent as a larger area of showery rain evolves towards midday and through the afternoon hours across much of England and Wales. This casts a lot of uncertainty over whether much lightning activity may occur beyond midday, and will significantly impact the placement of any pockets of surface heating. In theory there may be some sufficient insolation across East Anglia ahead of the occlusion, and across northern England and the Midlands behind the occlusion close to the elongated low centre, which may aid some deep convection in the afternoon hours - but confidence is low. Warming of the mid-levels behind the front across the Midlands may lead to fairly shallow convection during the afternoon/early evening hours. There may be an uptick in lightning activity across parts of Co Durham / Yorkshire / Lincolnshire from post-frontal convection late afternoon, but excessive cloud casts some uncertainty over this aspect.