A small low-pressure system will develop across the Bay of Biscay on Thursday night, moving northeastward and bringing some heavy showers for most of the UK and Ireland on Friday. Non-convective gusts, localised flooding, hail and frequent lightning are possible as this complex system moves northward, bringing localised disruption and damage.
During Friday early morning, an upper trough will introduce a warm theta-e air mass across the English Channel, moving northward across parts of southern England during the morning. This will provide energy for convective showers to develop, as this boosts the amount of CAPE ( around 500 J/kg) across central southern England. This might allow a few clusters of thunderstorms to develop across the English Channel, perhaps extending across central southern England, therefore a slight risk has been issued.
The main area of low pressure will move in toward the Celtic Sea on Friday evening, bringing torrential downpour across Ireland and Wales, 30-50 mm of rain are possible within 6 hours, and non-convective gusts up to 55 mph are possible, therefore severe risk of flood and gusts has been issued for these areas. Isolated thunderstorms are also possible but unlikely to be widespread in the West. At the southeastward of the main band of heavy rain, an upper trough will introduce another warm theta-e air mass to parts of East Midlands, Southeast England and East Anglia, MUCAPE of 500-800 J/kg allows elevated thunderstorms to develop across southeast England and East Anglia, there is another upper trough nearby which might produce more elevated thunderstorms across eastern coasts. Heavy rain (up to 50 mm within 3 hours) will bring localised flooding in places, so another severe risk has been issued.
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