Thunderstorms and rain are set to hit the UK across four days and bring to an end the warm weather which has seen temperatures soar to around 30C (86F) in parts of the country.
The Met Office has issued a yellow warning for most of England and the eastern half of Wales for storms on Wednesday and Thursday which could bring flash flooding, hail, strong winds and lightning strikes.
Forecasters said buildings could be damaged and the conditions could lead to delays on roads and rail.
Similar warnings have been issued for Friday and Saturday, but are more confined to eastern and south-eastern parts of England.
Some areas could see its average monthly amount of rainfall in just a few hours.
It comes after the hottest day of the year so far was recorded on Monday when temperatures soared to 29.7C (85F) in Teddington, southwest London.
Wednesday could see temperatures break the 30C mark before the storms begin to sweep in from Europe during the evening.
Sky News weather producer, Christopher England, said: “A scattering of thunderstorms, some torrential, will spread north across parts of England overnight, bringing a risk of disruption through power cuts and localised flooding.
“The south-eastern half of England is most at risk. The storms will clear to the North Sea during Thursday morning, but further storms are expected on Friday and Saturday.”
He added rainfall totals of 30mm per hour are possible in places, with up to 50mm over a couple of hours or so, but these will be quite localised. Some 50mm would be around the monthly average.
On Thursday, Northern Ireland and Scotland should see calmer conditions than other parts of the UK with some bright or sunny spells, but also a few showers over the west.