Warnings for thunderstorms and heavy showers have been issued by forecasters for Sunday, covering much of England and parts of eastern Wales.
The Met Office say there is a “small chance of flooding and disruption” in some areas as a result.
The yellow warning urging people to “be aware” comes into force from 04:00 BST, covering large swathes southern England, the Midlands and the north.
Forecasters warn thunderstorms and heavy rain are due to develop in the south of England on Sunday morning, moving northwards over the course of the day.
In England, an area in the centre of the country stretching from the Isle of Wight to Newcastle upon Tyne is covered by the warning.
In Wales, the warning is in place for Monmouthshire, Newport, Torfaen and Wrexham in the country’s east.
The Met Office said there is a chance of flooding, adding that “frequent lightning strikes and hail will be additional hazards” in southern and central England.
But the forecaster also warned the “extent of these thunderstorms is very uncertain, and many places will miss them”.