An occluded front associated with an upper low will bring extensive cloud cover and showery outbreaks of rain to many parts of the British Isles early on Sunday. These showers are expected to gradually clear to the north, potentially breaking up as the day progresses due to insolation (surface heating). This could result in the heating of the moist low-level airmass, especially from late morning onwards. Combined with a mid-level cold pool drifting NNE throughout the day, this will allow for 500-1000 J/kg of MLCAPE across parts of England and eastern Wales.
Numerous heavy showers and thunderstorms are likely to develop, particularly in convergence zones, most likely around Peterborough and Sheffield. Limited deep-level shear will prevent the development of severe and long-lasting thunderstorms, favoring pulse-type storms instead. However, a slight improvement in shear (DLS >20 kts) across northern England and parts of the East Midlands could support somewhat longer-lasting thunderstorms in these areas. As these cells mature and drift NNE, the greatest lightning risk will be in the Midlands, East Anglia, and Northern England. Diurnal heating could also trigger isolated thunderstorms in central southern England (most likely around Salisbury Plain) as the mid-level cold pool begins to move northward from 11z.
The strongest cells may produce hail (0.5-1 cm) and gusts of 40-50 mph. However, the lack of substantial shear will reduce the risk of severe weather. Additionally, low PWAT (precipitable water) will limit the risk of localized flooding, although some areas might still experience localized flooding due to the training effect of showers.
In Ireland, scattered heavy showers are also likely across central and southern parts due to diurnal heating and low-level convergence zones. However, the lack of CAPE will limit the amount of lightning in these regions.
You can download the KML file of the convective outlook here:
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