Millions of Britons are facing flash floods this weekend-up to 4 inches of rainfall in some areas.
From today to later tomorrow, both North Wales and North Wales yellow warnings for thunderstorms will be in effect.
But the British Meteorological Office said that almost any place could be hit by heavy rains-there could be an inch of rain within an hour.
Spokesperson Graham March said: "I think there will be heavy showers everywhere.
"We know the footprints of the places where we think the rainfall gets the most, but it's like a boiling pan.
"You will see bubbles appear-trying to determine the location of the next bubble is almost impossible."
The British Meteorological Office predicts that this unstable weather may continue until next week.
The yellow thunderstorm warning has now been extended to Saturday, and the Met Office urges Britons to stay safe.
Starting today, wind speeds are expected to reach 60 miles per hour, and in some areas, rainfall in one day may exceed one month.
Starting from Friday, the yellow weather thunderstorm warning will cover most areas of northern England and Scotland from 10 am, and rainfall in some areas will reach 100 mm.
This will continue until 9 am on Saturday-The Met Office warned that the combination of flooding and lightning strikes could pose a danger to drivers, homes and businesses.
The temperature on Saturday and Sunday will also be difficult to climb to 19C or above.
Previously, rainfall in parts of Western Europe hit a record high, and floods there last month killed at least 120 people.
The rivers in Germany and Belgium broke their banks, and entire towns and villages were destroyed.
Experts say that the high temperatures caused by climate change mean that extreme rainfall is more likely.
The bookmaker has now cut the odds for the wettest August on record in the UK in 2021 to 6-4.
Coral’s John Hill said: “We are going to face a difficult few days, with heavy rains in many parts of the UK, and we may have the wettest August on record.
"It has been a wet summer so far, and if things continue, it may become one of the wettest summers ever," Hill added.
But the heat wave will cause the temperature to soar in the second half of August, and the sun will start as early as next week.
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