The Yellow Warning could lead to flooding and disruptions.
The Met Office has issued a Yellow Weather Warning for thunderstorms in the UK.
The warning covers parts of England and Wales from midday on Monday to 10 pm.
Most of Wales is covered by the warning, as well as an area of England, stretching from the South West across to Kent, and up to Stoke-on-Trent.
Nearly 50mm of rain could fall in some areas, according to Sky News weather presenter Jo Wheeler.
She said: “Some areas may miss the showers, but where they occur, there’s likely to be hail, thunder, lightning, gusty winds and a temporary temperature drop.”
The Met Office said the rain could lead to difficult driving conditions and some road closures.
They warned that “scattered thunderstorms could lead to some flooding and disruption in places on Monday.”
Where flooding or lightning strikes occur “there is a chance of delays and some cancellations to train and bus services”, they said.
They have also warned that there is a “slight chance that power cuts could occur and other services to some homes and businesses could be lost.”
According to the Met Office, 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.”
