Parts of the UK could see almost a month’s worth of rain in the space of a couple of hours later.
The Met Office has issued a thunderstorm warning for much of Scotland and northern England which is in place from midday until 9pm on Thursday.
Heavy showers may cause flooding and travel disruption, with forecasters warning there is a small chance of fast-flowing or deep flood waters causing danger to life.
Meteorologist Emma Smith said 30mm of rain could fall in one hour, while 50mm could fall in two to three hours.
The average amount of rainfall in July for the UK as a whole is 70mm, while the July average for England is 55-56mm – meaning that almost a month’s worth of rainfall could fall in a couple of hours on Thursday.
The yellow thunderstorm alert from the Met Office warns there is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater and lightning strikes.
In places where there is flooding or lightning strikes, there is a chance of delays and cancellations to train and bus services.
Forecasters have also warned of difficult driving conditions, some road closures and power cuts.