Summary: A cold front will develop and bring heavy and squally showers, perhaps some isolated thunderstorms, moving from southwest England, expanding itself northeastward toward majority of England over the morning and early afternoon. Scattered showers with some hail and thunders are possible in the west overnight.
Convective Available Potential Energy (CAPE) ranging from 200 to 500 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 and eastern 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 morning, 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 England possibly encountering gusts of 50-60 mph. Intense rainfall and small hail are also potential concerns. There is a risk of tornadoes in central southern England, southeast England, southeastern Midlands and East Anglia during the late morning and early afternoon. When the cold front breaks into smaller segments, this can create 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 move eastward across the eastern parts of the UK, there will be another potential for clusters of heavy showers, boosted by strong shearing and weak CAPE (300-600 J/kg), to develop over the English Channel, Bristol Channel and west Scotland, possibly generating coastal gusts overnight. Low freezing level will also encourage small hail across these area. The post-frontal environment will be very unstable as cold air aloft overspreads relatively warm SSTs helping to generate numerous showers. These will pose the risk of occasional lightning strikes. The risk may increase over western Scotland towards midnight, bringing frequency lightning locally, hence a low ended enhanced risk has been issued.. Hail and squally winds will accompany many of the showers, perhaps gusting over 50mph locally, and an isolated tornado may also be possible.
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