Widespread thundery showers are anticipated across various regions of the United Kingdom and Ireland, driven by an unusually warm air mass supplying ample CAPE (Convective Available Potential Energy) to most of the area. Some models are indicating the possibility of up to 3000 J/kg of CAPE in western parts of England, an extreme occurrence in the UK's climate.
Southwest England/Wales:
Elevated thunderstorms are expected to develop in parts of southwest England and Wales overnight and in the early morning, potentially leading to clusters of lightning, especially in the enhanced risk zones of southwest England and south Wales. These storms could produce frequent lightning, localized flooding, and small hail. Moderate low-level and deep-level wind shears could sustain these elevated thunderstorms, possibly extending their activity into Wales. Consequently, an enhanced risk has been issued for substantial portions of southwest England and Wales. These elevated thunderstorms are projected to weaken by late morning.
Additional showers may develop in the late afternoon across inland areas of Wales and southwest England when the atmospheric cap breaks. CAPE is expected to widely exceed 2000 J/kg, possibly reaching 3000 J/kg in isolated areas. This suggests that thunderstorms may become quite intense when they erupt, potentially forming one or two supercells, although the risk of this occurrence is relatively low. These storms could result in localized flooding, large hail (up to 3.5 cm in diameter), and isolated tornadoes.
Northern Parts of Midlands/Northern England:
The remnants of the elevated morning thunderstorms are expected to weaken, but there may still be a few lightning strikes in parts of the West Midlands in late morning. A shallow atmospheric cap is in place, which could limit convective activity, but it is likely to break by mid-afternoon. Severe thunderstorms are likely to form rapidly due to the high CAPE values (2000-3000 J/kg), moving northeast toward the North Sea. Moderate low-level and deep-level wind shears will support the longevity of these thunderstorms, and as a result, some areas, particularly in the high-risk zone, may experience multiple severe thunderstorms characterized by frequent lightning. The strongest cells may produce large hail, up to 5 cm in diameter, potentially causing localized damage to infrastructure. There is also a possibility of one or two supercells forming in the high-risk area, possibly moving from Nottingham toward the North Sea. This would carry a risk of tornadoes and very heavy downpours (50 mm within 3 hours), posing a threat of localized flooding. Strong gusts are also possible in the strongest cells as well.
Central Southern England:
There is some uncertainty regarding the initiation of thunderstorms in the afternoon in this region. However, certain high-resolution models suggest that the atmospheric cap could break early in the afternoon, potentially allowing for the formation of a Mesoscale Convective System (MCS) across the North Wessex Downs, with a northeastward trajectory into Lincolnshire. While this scenario is currently deemed unlikely, it is being closely monitored, and the enhanced risk zone may be expanded if necessary.
Ireland/Northern Ireland:
Strong, potentially severe thunderstorms are forecasted to develop across inland parts of Ireland and Northern Ireland in the afternoon. CAPE values are expected to exceed 1000 J/kg, supporting the formation of robust and frequent thunderstorms. These storms may move slowly, elevating the risk of localized flooding, with more than 60 mm of rain possible within a 3-hour period. There is also a possibility of small hail. However, the limited deep-level wind shear may prevent these thunderstorms from being long-lived.
Please note that updates may be issued early Sunday to provide the latest information on the evolving weather situation.
You can download the kml file of the convective outlook here
(You can upload the file to windy.com to have the graphic overlay)
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