On Wednesday, an upper low is expected to form over Germany and Benelux, ushering in a relatively warm Theta-E airmass along the northern and eastern parts of the occluded front.
Forecast models indicate relatively high CAPE values (700 - 1500 J/kg) late on Wednesday, a rarity for May according to climatology. By late afternoon/early evening, a shortwave from the southeast will trigger the development of a wave along the frontal boundary, increasing the potential for dynamic rainfall. Isentropic upglide on the northeastern flank of the frontal wave will lead to scattered elevated thunderstorms over southeast England during the evening hours. Strong deep directional and speed shear will facilitate organized thunderstorms, fueled by warm, moist inflow from easterly low-level winds. The potential for upscale growth into a Mesoscale Convective System (MCS) exists as the thunderstorm complex drifts northwest across the Midlands. Hazards associated with this complex include hail, gusty winds, frequent lightning, and localized surface water flooding.
-ECMWF 28/04/2024 12z CAPE (J/kg)
-ARPEGE 28/04/2024 12z CAPE (J/kg)
-ECMWF 28/04/2024 12z DLS (kn)
Strong deep directional and speed shear will facilitate organized thunderstorms, fueled by warm, moist inflow from easterly low-level winds.
-ECMWF 28/04/2024 12z Entire Atmosphere Precipitable Water (mm)
High EAPW value might increases the chance of localised flooding
This setup is unusual for the UK, as most plume events originate in north France and turn elevated upon reaching the UK. However, in this event, thunderstorms are expected to initiate across East Anglia and the Benelux area.
Given the strong background signal, there is potential for an enhanced/moderate risk to be issued, though pinpointing the exact area is challenging at this time.