On Saturday, a low-pressure system will develop over the Celtic Sea, ushering in a series of frontal systems to the southern UK. This will introduce a relatively warm theta-E air mass due to a warm front.
During the late afternoon, the warm front may trigger thunderstorm development, particularly in southwestern England and Wales. However, the limited Convective Available Potential Energy (CAPE) and a saturated profile will restrict activity. Elevated thunderstorms may form, sustaining their thundery nature over central southern England due to moderate low-level and mid-level wind shear. Slow-moving storms could lead to significant rainfall accumulation and localized flooding.
In the early night, thundery showers are expected behind the warm front as the profile becomes less saturated and the increased amount of CAPE (800-1000 J/kg). These thunderstorms will move northeast, potentially generating potent thunderstorms in some areas. Strong shearing conditions increase the likelihood of isolated supercells with rotating updrafts. This setup favours the production of hail up to 1 cm in diameter, intense rainfall (up to 50 mm in 6 hours), and very strong gusts (possibly exceeding 80 mph locally). Coastal flooding may occur due to high tides and strong coastal gusts.
A convective outlook for Saturday will be issued on Friday, October 27, 2023, at 9 p.m. to provide further guidance.
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