A warm front is poised to usher in heavy downpours and elevated thunderstorms during late morning and early afternoon across portions of southwestern England and the southern regions of Wales. Significant horizontal wind shear at lower altitudes will cause these thunderstorms to move sluggishly and have a relatively brief lifespan. The gradual storm movement will lead to the intersection of the downdraft with the updraft, resulting in a slight reduction in storm intensity. Within the moisture-rich environment where these storms originate, rainfall may become intense, albeit for a short duration.
In the early night, a trough will approach southeastern England, potentially generating potent elevated thunderstorms in certain areas. The strong shearing conditions increase the likelihood of isolated supercells characterized by solitary rotating updrafts. These conditions are optimal for nurturing such rotating updrafts. The presence of significant speed shear facilitates swift storm movement, effectively maintaining a separation between the updraft and downdraft. At the same time, directional shear plays a pivotal role in inducing rotation within the updraft, endowing these cells with the potential to produce marginally severe size hail (up to 2 cm in diameter), intense rainfall (up to 50 mm within 6 hours), and strong gusts (up to 55 mph).
At the same time, the potential for additional surface-based thunderstorms emerges. These storms initially develop in Dorset and progress northward into Somerset, Wiltshire, and sections of the West Midlands as a trough moves northeastward. There's a possibility that this trough may even extend into northern areas of Lincolnshire and Yorkshire overnight. However, the absence of significant wind shear will confine these thunderstorms to localized and short-lived events.
Thunderstorms in South Wales, Somerset, and Gloucestershire may exhibit greater activity due to higher levels of 3CAPE (170-190 J/KG). This heightened instability could potentially result in localized heavy rainfall (up to 40 mm within 6 hours), raising the risk of flooding in these areas.
As a cold front approaches Wales overnight, a sharp temperature contrast will allow sporadic thunderstorms to form in parts of Wales and southwestern England. Elevated levels of 3CAPE (>150 J/Kg) may foster isolated lightning within thunderstorm cells.
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