Forecast Details

Upper trough crossing the UK overnight will start to amplify south and disrupt across western Europe from Friday and through the weekend. Upper and collocated surface low will become slow-moving over the south N Sea, the surface low deepening off the north coast of Holland, with a strengthening Nly flow spreading S across the UK.

Cold mid-levels associated with upper trough over UK will produce steep lapse rates across S Wales, S England and E Anglia – where moisture and surface heating will be greatest. Further north, an occluded front slowly sinking south from N England/N Wales will produce cloud and rain limiting isolation and thus instability. While across Scotland airmass will be generally too stable for thunderstorms. Surface heating in sunny spells across the S England and E Anglia likely to yield between 400-700 j/kg CAPE, which will support the development of scattered heavy showers and thunderstorms. A wind convergence zone is indicated to move S across S England during the afternoon and will be the main focus for thunderstorm development, otherwise weak vertical shear will mean thunderstorms will be scattered elsewhere and generally short-lived. Weak winds aloft and surface convergence will lend to stronger updrafts perhaps rotating to produce funnel clouds or perhaps even a brief weak tornado – particularly towards the S coast. Slow-moving nature of storms may produce localised flooding – particularly where storms train along wind convergence.