The Met Office has issued a yellow weather warning for two days of rain and thunderstorms around the UK.
A warning for rain is in force in the south of the country from 4pm today until 3am tomorrow.
Forecasters have warned that wet and windy weather is likely to bring some disruption overnight.
Roads are also expected to be wet, with spray and flooding possible, as well as journeys taking longer than usual.
Another yellow warning for thunderstorms covers south-western England, Wales and parts of the Midlands and is in force until 12pm today.
It reads: "A brief period of heavy rain, thunderstorms and very gusty winds may cause some disruption on Wednesday morning."
The Met Office said that there is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds.
There is also a slight chance that power cuts could occur and that some trees could be damaged by strong winds.
Meanwhile, an Arctic chill could bring up to six inches of snow and the coldest day since spring, forecasters have said.
The cold snap is expected to hit parts of the country with snow likely to fall in higher regions after experts predicted plunging temperatures caused by a polar vortex.
Snow could appear on mountain parts of Scotland on Thursday, with temperatures possibly dropping to 6C by the weekend.
John Hammond, former BBC weatherman and meteorologist for Weathertrending, said: "After a very mild few days, much colder air will arrive from the north later this week, which may bring some snow to the Scottish mountains.
"That cold spell may not last all that long, but frost, and eventually snow, will probably figure more frequently in our forecasts before too long."
Met Office meteorologist Sarah Kent said there are increasing chance of rural frosts on Thursday.
She said: "If you’re out mountaineering, don’t be surprised if you get wintry weather."
UK 5 day weather forecast
Today:
Windy with rain and showers for many, particularly Wales, southwest and central England where lightning and hail likely, mostly during the morning. Northern Ireland, southern Scotland and far north of England mostly dry. Warm in southeast but cooler in north.
Tonight:
Heavy rain running east across southern England with coastal gales possible. Much of Wales and central England dry. Windy with rain and showers over Scotland moving south. Turning colder.
Thursday:
Much colder across entire UK and feeling cold in the north and east with strong winds and gales in the far northeast. Showers feeding into northern and some western parts.
Outlook for Friday to Sunday:
Cold start Friday, with scattered showers in the north. Many other areas dry, though breezy. Dry and cold start again Saturday, before rain and milder weather spreads from the west.
