“The heaviest rain is likely to affect central southern England, south-east England and the Midlands on Friday night before moving to northern England and Scotland by Saturday.
There could be as much as a month’s worth of rain falling in just a few hours and this would lead to flash flooding. Frequent lightning, large hail and gusty winds are additional hazards that would bring transport disruption.”
https://www.bbc.co.uk/weather/articles/cn7d5221le7o