Britain is facing a severe risk of flash flooding as intense thunderstorms are predicted to bring a month's worth of rain to drought-stricken areas. The Met Office has issued yellow warnings across England and Wales for Wednesday and Thursday, with slow-moving heavy showers and thunderstorms expected to move northwards.
Today's thunderstorm alert, active until 10 p.m., covers much of England and parts of Wales. Forecasters anticipate up to 30 millimeters (1.2 inches) of rain could fall in less than an hour in some locations, with potentially up to 50 millimeters (2 inches) within two to three hours. Tomorrow's warning, running from 6 a.m. to 10 p.m., will encompass all of Wales and similar areas of England, excluding London and the Southwest. Up to 30 millimeters of rain in three hours is expected widely, and some areas, particularly east-facing high ground, could see over 50 millimeters in three hours and more than 75 millimeters (3 inches) in a 12-hour period. Hailstones up to 2 centimeters (0.8 inches) are also possible.
Met Office chief forecaster Steve Willington noted that warm and humid air is contributing to the risk of heavy showers and thunderstorms. "Some places could see significant amounts of rain falling in a short period of time, bringing the potential for localised flooding, travel disruption and frequent lightning," he stated. The forecast for Thursday also indicates a possibility of prolonged rainfall in some areas due to slow-moving, thundery rain.
These warnings follow a prolonged period of hot and dry weather that has led to drought conditions in nearly three-quarters of England and all of Wales. Rivers and reservoirs have been running low, with some areas experiencing over two months without significant rainfall. Last month was the driest July on record for England, with some parts of the south-east receiving minimal rainfall throughout August.
Road safety experts have cautioned drivers about the increased risk of skidding on roads that have accumulated oil, fuel, and rubber deposits during the dry spell. The initial light rain can mix with these substances, creating greasy conditions. "If heavier rain arrives, motorists may have to contend with the danger of flash floods in some areas," said RAC road safety spokesman Rod Dennis. Drivers are advised to reduce speed, increase following distance, and be prepared for rapidly changing road conditions, including reduced visibility due to heavy rain and spray.
London Mayor Sir Sadiq Khan warned of severe flash floods in the capital, with up to 50 millimeters of rain potentially falling in a few hours, equivalent to almost the average rainfall for August. He urged residents to check their insurance coverage and take preparatory measures.
The Met Office has also advised securing outdoor items such as bins, garden furniture, and temporary structures against potential gusty winds. Unsettled conditions are expected to persist into the weekend, with further showers and rain possible.
Forecasters have also warned of potential storms and rain this autumn and winter, partly influenced by an 'unprecedented' El Niño event, which is expected to be one of the strongest on record.