A yellow warning for multiple rounds of heavy showers and thunderstorms has been extended to include much of Wales.
The warning area covers mainly inland parts of Wales and runs throughout Thursday, 1 August.
The Met Office says 'Multiple rounds of heavy showers and thunderstorms may lead to some disruption'.
The yellow warning adds: "An area of showery rain is likely to develop and move northeastwards across parts of Wales, the Midlands and northern England.
"This will be heavy and perhaps thundery at times, persisting through Thursday morning before easing towards midday. Some areas could receive rain accumulations of 25-50 mm over the course of a few hours.
"Scattered heavy showers and thunderstorms are then expected to develop through Thursday afternoon and evening across parts of central, southern and eastern England, and perhaps also south Wales.
"These have the potential to produce 50 mm or more in 1-2 hours, along with gusty winds, large hail, and the risk of surface water flooding."
The warning area avoids coastal parts of west Wales, but does cover towns such as Machynlleth, Dolgellau and Blaenau Ffestiniog.
Spray and sudden flooding could lead to difficult driving conditions and some road closures and power cuts might occur.
The Met Office adds that flooding of homes and businesses could happen quickly and fast flowing or deep floodwater is possible, causing a danger to life.
Met Office Deputy Chief Meteorologist David Oliver said: “On Thursday there is a signal for some potentially very heavy thunderstorms to develop. There are still details to confirm during this period, but in any event there is a chance of some impacts on each day, especially Thursday.
“The heaviest showers on Thursday could result in 20-30mm of rain within an hour, with daily totals possibly reaching as high as 90mm if multiple showers impact the same location. Lightning and hail present additional hazards, with disruption likely for some. This is a developing element of the forecast, so it’s important to stay up-to-date with the latest outlook in the coming days.”