A shortwave associated with a cold air mass aloft will move westward into England and Wales on Friday. As the cold air at mid-levels interacts with the environment, the lapse rates will steepen throughout the day, leading to cooler temperatures aloft. At the same time, a warm and humid theta-E plume will be introduced at lower levels, creating an increasingly energized atmosphere. Convective Available Potential Energy (CAPE) is expected to build up, peaking at over 1000 J/kg across Central-Southern England and parts of the Midlands. Strong 0-3 km CAPE (around 250 J/kg) suggests that any thunderstorms that develop will be accompanied by frequent lightning.
The upper trough across western Germany will shift westward overnight, possibly triggering elevated thunderstorms in the early morning over parts of East Anglia and the East Midlands. As these morning showers dissipate by early afternoon, convection will develop across southern England, especially along a convergence zone. High-resolution models indicate the main convergence zone will form along the southern coasts and the M4 corridor, driven by a combination of sea breezes and northeasterly winds.
Isolated cells are likely to develop easily due to the unsaturated profile, increasing the risk of localized flooding from training storms. Strong low-level shear (20-30 knots) could support rotating updrafts, and with the presence of a convergence zone, there is a possibility of supercells or even tornadoes, especially in areas under HIGH risk. Steep lapse rates and strong CAPE could also lead to hail formation, potentially up to 2.5 cm in diameter. Overnight, most high-resolution models have shifted toward a more severe scenario, indicating a severe thunderstorm, possibly a supercell, moving westward and intensifying during the mid to late afternoon. Areas in Hampshire, Wiltshire, and Somerset are most likely to be impacted by these severe thunderstorms or supercells. Localized rainfall could reach 20-40 mm within three hours, heightening the flood risk. Additionally, strong gusts (up to 55 mph) are expected within the storm. Further severe thunderstorms are expected to develop south of the main system, affecting Dorset and Devon during rush hour.
You can download the kml file of the convective outlook here:
Comentarios