In the morning, shallow convection may develop in southern and western Ireland, where Convective Available Potential Energy (CAPE) ranging from 100 to 300 J/kg could energize the cold front, leading to the formation of one or more squall lines. Isolated lightning strikes are possible in the southern regions of the cold front as a slightly warmer air mass is introduced by southerly winds. Gusty winds within the squall line could cause localized damage.
As the cold front crosses the St George's Channel in the early afternoon, it is expected to become more active, with isolated thunderstorms developing within the cold front. Coastal areas may experience gusts of 60-70 mph, with inland areas of Wales and southwest England possibly encountering gusts of 50-60 mph. Intense rainfall and small hail are also potential concerns. There is a risk of tornadoes in southwestern England and parts of Wales during the late afternoon, particularly in Devon, Somerset, Cardiff, and Bristol. Orographic lift across Merthyr Tydfil, Dartmoor, and Exmoor may cause the squall line to break into smaller segments, creating conditions for rotating updrafts and the development of weak tornadoes.
Research on Synoptic-Scale Environments and Precipitation Morphologies of Tornado Outbreaks from Quasi-Linear Convective Systems in the United Kingdom indicates that tornado outbreaks, defined as days with three or more tornadoes, often occur in convective storms with heavy precipitation over a line exceeding 100 km. This suggests that tornadoes in such a setup are not uncommon.
While the squall line is expected to weaken overnight while moving eastward across the eastern parts of the UK, there is still potential for clusters of thunderstorms, indicated by shallow CAPE (200-400 J/kg), to develop over the English Channel and the south coasts, possibly generating coastal gusts overnight. Meanwhile, higher CAPE (500-700 J/kg) is likely to develop behind the cold front, especially across southwest England and Wales, where clusters of thunderstorms might form along strong shearing, potentially producing very strong gusts (55-65 mph) along the Bristol Channel once again.
You can download the KML file of the convective outlook here:
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