Severe thunderstorms are expected in Cornwall today as the county will be forced to endure a brief break from the searing heatwave.
Then, a yellow weather warning is in place from Sunday morning at 3am until 3pm, with as much as 80mm of rainfall expected to fall.
Torrential downpours, large hail and strong, gusty winds could also become hazardous, with yellow warnings for rain and wind in place.
Today (Saturday) will see a mixture of thunderstorms, showers and strong winds take hold throughout the day, with torrential rain moving in overnight and expected to last until the early hours of Monday morning.
The Met Office is predicting that thunder showers could take place at 9am, 11am and 2pm in Truro, although this will vary from town to town. The thunder storms will be disrupted by showers and brief periods of sunshine.
Today's Cornwall forecast according to Met Office:
A mixture of sunshine and showers, these driven on by a brisk and gusty southwesterly wind. Some of the showers could be heavy at times. Feeling much cooler and fresher than recent days, especially in eastern areas. Maximum temperature 21 °C.
Showers largely dying away, leaving a brief drier interlude with winds easing. Heavy rain, accompanied by coastal gales, will move into Cornwall around midnight, before spreading northeast across all parts. Minimum temperature 15 °C.
Heavy rain and strong to gale force winds in the morning. The rain will become rather more showery in the afternoon, with winds easing a touch. Maximum temperature 22 °C.
Below we answer some of the key questions around thunderstorms
Why do thunderstorms happen during heatwaves?
The two vital ingredients for a thunderstorm are instability in the atmosphere and moisture, Grahame Madge at the Met Office said. Thunderstorms take place when there is more humid air in the system, which is the case at the moment during the ongoing heatwave. They tend to develop later in the afternoon after the progressive heating during the early part of the day, Mr Madge added.
Has this happened in the UK before?
Yes. The 1976 heatwave and dry spell was occasionally interrupted by violent storms. Met Office archives reveal that "thunderstorms occurred in many districts" during the first half of July 1976, with heavy rain causing local flooding on several days. On July 12 1976 a man was killed at Clapham near Bedford when the cab of his lorry was struck by lightning. The same day, 64.8mm of rain was recorded at Sudborough in Northamptonshire, while at Ashover in Derbyshire 15mm of rain fell in just 12 minutes.
How do thunderstorms form?
Thunderstorms are created by the intense heating of the earth's surface, and are most common in parts of the world where the weather is hot and humid. The Met Office says thunderstorms develop when the atmosphere is unstable - when warm air exists underneath much colder air.
Are thunderstorms common?
Thunderstorms are common occurrences on Earth, according to the Met Office. It is estimated that a lightning strike hits somewhere on the Earth's surface approximately 44 times every second, a total of nearly 1.4 billion lightning strikes every year.
What actually is thunder and lightning?
Thunder is the sound produced by the rapid heating of air by a lightning strike, and lightning is a huge electrical discharge that flows between clouds, from a cloud to air, or from a cloud to the ground, according to the Met Office descriptions.
Is there a risk of flooding during the UK thunderstorms? And if so, why?
The yellow weather warning says flooding of homes and businesses could happen quickly, with damage to some buildings from floodwater. There are flood alerts in place in the Midlands, South East England and North East England. Within a thunderstorm there is huge capacity to suddenly release lots of moisture "incredibly intensively", Mr Madge said, describing the phenomenon as "one of the most dramatic and most intense" weather events that we get in the UK. When the conditions are created for a large volume of water to hit the hard, dry ground - caused by a prolonged dry spell - floods are possible. Mr Madge said flash flooding can cause draining systems to become overwhelmed with the sheer volume of water. "It's because it's a high volume of rainfall falling incredibly quickly," he said.
Is there anywhere in the UK where thunderstorms are most common?
In the UK thunderstorms are most common over the East Midlands and the South East, according to the Met Office.