Thunderstorms and heavy rain are forecast to lash the UK today (Sunday), triggering warnings of flooding and travel disruption.
The Met Office has issued a yellow thunderstorm warning for large swathes of England and Wales on both Sunday and Monday.
Flooding could cause roads to close, while extreme weather may damage buildings and cause power cuts and cancellations to train and bus services.
Forecasters also expect this week to be much cooler, with top temperatures reaching the mid-twenties.
In Bristol, the BBC is predicting 16 hours of thunderstorms on Monday, starting at 6am and lingering until 9pm.
The Met Office's forecast is less grim. The authority says downpours are likely for most of the day but does not predict lighting and thunder.
Matthew Box, a Met Office forecaster, said: "The risk of thunder will start to push further north on Sunday, with central parts of England and Wales facing heavy rain and the chance of flooding."
On Saturday, a shopping centre was evacuated and roads were submerged as parts of Essex were hit by severe flooding.
Residents of Chelmsford described scenes of "carnage" and said "half the city seems to be underwater" after it was swamped by a heavy and slow-moving thunderstorm at about 5pm.
UK weather forecast
Sunday:
Showery rain across central parts moving northwards and dying out. Further heavy showers and thunderstorms breaking out in the south. Warm in the south and northwest, cool in the northeast.
Outlook for Monday to Wednesday:
Monday, northern Scotland sunny, showers in the east. Elsewhere, sunny intervals, showers or thunderstorms. Tuesday, sunshine and showers, heavy in the north. Wednesday, drier in the south, showers further north.
