The Met Office has issued a yellow warning for thunderstorms for most of the UK for the whole of Monday up until midnight.
It said that thunderstorms may cause flooding and lightning strikes which could cause flooding and disruption to train and bus services, and there is a chance of power cuts and road closures.
The warning covers the north west and part of the north east of England, as well as the East Midlands, the West Midlands and Yorkshire. Eastern and central areas of Scotland are also at risk of thunderstorms and all of Wales is affected.
The Met Office said between 30mm and 40mm of rain could fall in an hour widely, and in local areas between 60mm and 80mm of rain could be seen, potentially sparking flash flooding.
Met Office spokesperson Stephen Dixon told Yahoo News UK on Monday: "Thundery outbreaks are expected for parts of Wales, northern and central England, as well as much of Scotland, through the day today.
"While the extent of these thundery outbreaks will be hit and miss, some places may see 30mm to 40mm rainfall in an hour, with 60mm to 80mm possible where thundery outbreaks converge.
"Lightning will be an additional hazard and the greatest chance of impacts is likely in eastern Scotland this afternoon, as well as parts of Wales and the West Midlands."
The rest of the week will also see unsettled conditions, although temperatures will remain in the low 20s, with the prospect of more thunderstorms from Thursday onwards.
"A mixture of showers and cloud is likely for much of the country on Tuesday and Wednesday, though there will be drier interludes at times," said Dixon.
"There’s much uncertainty from Thursday, with a large degree of possible scenarios in weather models, but the most likely scenario at present is for a plume of warmer air to bring widespread cloud and outbreaks of rain, which could carry a thundery element with them."