A thunderstorm warning has been issued for parts of Britain - with fears heavy rain could cause floods and travel chaos.
The Met Office said large swathes could be hit by wild weather - although "many places" could miss the worst of it.
Warnings have been issued for much of England and parts of Wales, running from 12pm to 10pm on Saturday.
Forecasters have said there is a "good chance" driving conditions will be affected, leading to longer journey times.
Delays to train services are also possible, the Met Office said, and some short term losses of power may happen.
A weather alert added that "flooding of a few homes and businesses could occur".
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Alex Deakin, from the Met Office, said: "Saturday will see fairly heavy showers in some places. Rainfall is coming from an area of low pressure slowly edging towards the UK on Friday.
"There will be rain broadly speaking moving from West to East.
"Before it arrives some bright spells in eastern parts of England and we are likely to see some sunny spells in Northern Ireland and South Wales ad South East England with temperature highs of 24C in the South East.
"Otherwise a lot of cloud and rain and it will probably feel quite cool."
But, in better news, experts predict a warm front will come in on Monday bringing with it more sunshine and warmer temperatures of up to 27C.
The warm weather is expected to last into next week.
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The weekend washout comes amid the Met Office's warning that a heatwave is unlikely to happen - despite hopes the Bank Holiday weekend would be scorching.
Forecaster Steven Keates said previously: "This summer has certainly been unremarkable and pretty bland. It's not going to be remembered for warmth.
"We've had flooding, some parts of the country have seen double their average rainfall, and temperatures have been average.
"A heatwave is not on the cards either."
Check out the latest forecast below.
Today:
Rain, some heavy, soon reaching Northern Ireland, spreading to parts of Scotland and then northwest England and northwest Wales. Elsewhere, mostly dry, just an isolated light shower; still plenty of cloud for most places, although a few sunnier, warmer spells.
Tonight:
Rain continuing across many western and northern areas, heavy at times, perhaps especially in the southwest later. Northern Ireland drying up, and southeastern areas largely dry. Mild and rather humid.
Saturday:
Fine, warm start in the southeast but wet weather in some western areas edging eastwards. Slightly brighter skies with sunny intervals but scattered thundery downpours following to some areas later.
