The Met Office has issued a severe weather warning for South Yorkshire for this evening and overnight.
Isolated heavy, and possibly severe, thunderstorms are expected to develop on Friday evening across parts of southern and southwest England.
These are likely to become more frequent later and spread northwards across Wales, the Midlands and northern England overnight, and into southern Scotland by the early hours of Saturday.
The Chief forecaster's assessment states: "On Friday evening another hot and increasingly humid airmass is expected to spread northwards from the continent.
"This airmass looks conducive to the development of isolated thunderstorms during the evening across southern and southwest England which are likely to become more frequent overnight as they spread northwards towards Scotland.
"With large amounts of energy again available in this atmosphere storms could be severe, with torrential downpours, hail and squally gusts of wind. 30 mm of rain is possible in less than an hour, with as much as 50 mm possible in 3 hours very locally.
"Large uncertainty remains regarding areas most at risk from storms, and many areas will miss these altogether, staying largely dry.
"However, where they do develop, disruption is possible. The most likely area for disruption is considered to be Wales, parts of the Midlands and northern (especially northwest) England, but a lesser risk extends around the periphery of this region."