Weather warning for thunderstorms issued as dry conditions increase flash flood riskImage source, Getty Images/Leon NealImage caption, Thunderstorms brought flash flooding to London 17 August 2022 following summer heatwavesPublished2 hours agoIntense thundery downpours are set to bring a risk of flash flooding to parts of the UK Friday night and into Saturday. The hardest hit communities could see well over a month's worth of rain falling in the space of a few hours leading to a significant risk of disruption. Yellow thunderstorm warnings have been issued by the Met Office with torrential rain bringing around 20-30mm (about an inch) in an hour but as much as 60-90mm of rain in a few hours. This is well over a month's worth of rain falling in a few hours for the biggest storms. Soils have been baked dry especially across England and east Wales after three successive summer heatwaves. Heavy rains cannot easily be absorbed by dry soils, external with water tending to run off rapidly bringing a greater chance of seeing some areas of flash flooding. Which areas will be most affected?Image caption, Met Office yellow thunderstorm warning for Friday night and SaturdayAn area of low pressure is set to develop in France as cool air high in the atmosphere pushes over very warm and moist air near the surface. This combination makes the atmosphere unstable with air rising upwards to form thunderstorms. These storms will initially develop in France before heading northwards across the UK. 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.This area of rain could become slow-moving across northern Scotland during Sunday, with a threat of some flash flooding. Low pressure looks set to take hold of the weather across the UK on Sunday and Monday with further widespread showers and thunderstorms likely. Thunderstorms always bring large variations in rainfall amounts from one place to the next, but some again could bring heavy downpours with a few areas of flooding.Why drought can lead to dangerous floodingWill this heavy rain affect the hosepipe bans?Image source, PA MediaImage caption, Low water levels at Agden Reservoir near SheffieldHosepipe bans have been announced over recent weeks affecting millions of people as drought is declared across more areas of the UK, external. According to Helen Wakeham, Environment Agency Director for Water and National Drought Group chair: "This has been the driest start to the year since 1976."Because the rain will be very heavy in places, it will runoff rapidly, perhaps overwhelming local sewers, before heading to the rivers and out to sea. At this time of year, any rainwater that does make it into the ground will just be taken up by growing plants and trees, so won't affect groundwater levels much. To see a substantial recovery in reservoir and groundwater aquifer levels we'd need a more sustained spell of much wetter weather, this is typically what we see during our autumn or winter, so the hosepipe bans will likely last for the rest of summer and probably into the first part of autumn too.More on this storyIs there a hosepipe ban in my area? What you need to know as restrictions widenPublished2 hours agoMore hosepipe bans possible as UK drought threat buildsPublished2 days agoMonthly OutlookPublished1 day ago