Thunderstorms could hit today as parts of the UK brace for a washout.
The south of England is set to see downpours later, which also brings the threat of lightning.
Up to 30mm of heavy rain will be dumped in some areas and the Environment Agency has warned of possible flooding.
Alerts are in place in 15 locations, including High Wycombe, Hursley and the Salisbury Plain area.
Showers are set to become patchier as the day goes on, although rising temperatures could bring more rain.
However, conditions are set to be much drier and brighter in the north, with some sunshine in the west.
The weekend is also set to bring more chilly weather, with some Brits set to wake up to frost.
Saturday will see the mercury struggle to get into double figures in much of the country, although there will be highs of 13 to 14C in the south, and in the west of Scotland.
Giving the latest forecast, a Met Office spokesman said there will be a "significant north/south contrast in our weather" today.
"In fact for southern counties of England as well as south Wales, [there is] the threat of thunderstorms moving up from France overnight," he continued.
"These will be hit and miss as is always the case but the threat from lighting is very real and for the south east of England in particular.
"Further north, Scotland, Northern Ireland, and northern England [will see] clear spells.
"A chilly start to Saturday with a touch of frost in places, otherwise a largely sunny day to come here north of around Cumbria.
"Further south a lot of low cloud, a gloomy day to come.
"Heavy rain early on generally petering out but remaining fairly chilly under that layer of cloud and in the easterly breeze further north
"In the far south temperatures will rise through the afternoon perhaps sparking a further heavy shower or two. But for most it turns dry into Saturday night."
UK five-day weather forecast
Today:
Much of England and Wales cloudy and cool with showery outbreaks of rain, perhaps heavy at first. Rain should become patchy, but any brighter spells might just trigger a heavy shower. Northern areas fine, best of sunshine in the west.
Tonight:
Northern Britain mostly fine, with some cloud in the east but clear spells and patchy frost further west. Southern and western areas cloudier with the odd shower and mostly frost-free.
Sunday:
Mostly sunny in the north. The odd shower could still occur in the southwest but an emphasis on dry weather, with brighter skies slowly filtering further south and west. Warmer.
Outlook for Monday to Wednesday:
Most places dry with plenty of sunshine. Just a small chance of a few showers affecting the far southwest at first. Windy across the south for a time. Becoming warmer.
