Berkshire has been placed under a yellow weather warning for heavy rain until the end of Friday.
Occasionally heavy rain is expected to reach the south west of England on Thursday evening before spreading across much of England and Wales on Friday.
The yellow warning warns of increased spray and flooding on roads, and predicts some bus and train services will probably be affected.
A spokesperson for the Met Office said: “Rain, heavy and persistent at times, is expected to develop through Thursday evening, before affecting much of England and Wales through Friday.
“Across the south of the area, it is possible that some thunderstorms may break out, and these could bring 20-30 mm of rainfall in a couple of hours.”
All parts of the country will turn much cooler by the weekend, with daytime temperatures potentially up to 10C colder than earlier this week across southern England.
Met Office Deputy Chief Meteorologist, Brent Walker, added: “By the weekend we expect all regions of the UK to be in the cold air mass and overnight frosts are possible.”
