VALID 06:00 UTC Wed 06 Mar 2019 - 05:59 UTC Thu 07 Mar 2019
ISSUED 21:18 UTC Tue 05 Mar 2019
ISSUED BY: Dan
An upper trough will slowly migrate eastwards across Ireland on Wednesday, placing England and Wales on the forward side. A warm, moist low-level airmass will exist beneath cool mid-levels, creating reasonably steep mid-level lapse rates and a few hundred J/kg CAPE.
Behind the main frontal precipitation, deep convection will likely already exist over the Irish Sea / west Wales / SW England on Wednesday morning, forced by a shortwave behind the surface cold front. This zone will be the primary focus for some sporadic lightning activity as it continues to track northeastwards across Wales / Midlands / N England through Wednesday daytime, aided by diurnal heating and low-level convergence.
Primary concern is rather saturated profiles / excessive cloud, which will tend to limit buoyancy somewhat. However, despite marginal instability the upper forcing coupled with strong shear should be enough to produce sporadic lightning strikes as scattered showers migrate NE-wards across the area. As such, have introduced a low-end SLGT to cover this risk. The strongest cells could produce hail up to 1.5cm in diameter.
Farther southeast, convective depth and instability will be somewhat limited, but even here a few isolated lightning strikes are possible, especially later in the afternoon - but coverage probably not widespread enough to warrant an upgrade to SLGT.
Shower coverage and intensity will gradually reduce during the evening hours as daytime heating subsides, with the focus for any isolated lightning activity overnight primarily confined to SW / W / NW Ireland.