Updated

Updated · bbc.co.uk · Aug 3

Met Office Issues 9-Hour Thunderstorm Warning for Northern Ireland as UK Heatwave Tops 30C

Updated

Updated · bbc.co.uk · Aug 3

Met Office Issues 9-Hour Thunderstorm Warning for Northern Ireland as UK Heatwave Tops 30C

Q: If dry, scorched ground cannot absorb sudden downpours, could this summer’s biggest flood risk come after the hottest days?

Yes. The biggest immediate flood danger can arrive just after the hottest days, not during them, because prolonged heat can harden and dry the ground so much that intense rain runs off the surface instead of soaking in. That is why forecasters are warning about flash flooding even though much of England remains very dry. The Met Office says some areas could see 20-30mm of rain in an hour or two, especially in Northern Ireland and parts of northern and western Britain. On baked ground, that kind of downpour can quickly overwhelm roads, drains and low-lying areas. The risk is most acute from slow-moving summer thunderstorms rather than steady all-day rain. Heat helps build powerful storm clouds, and warmer air can hold more moisture, increasing the chance of short, intense bursts of rain, hail and strong winds. In those conditions, surface water flooding can develop fast even where rivers stay relatively low. This does not mean every hot area faces the same flood threat. Southern and eastern England may stay largely dry as the front passes, while northern and western areas are more likely to catch thunderstorms. But where storms do hit after drought, the “flood-in-a-drought” pattern is well recognised by meteorologists and hydrologists. So the main near-term risk is not a classic widespread river flood. It is localised flash flooding triggered when a heatwave is broken by sudden heavy rain falling on scorched, water-resistant ground.

3 articles · Updated · bbc.co.uk · Aug 3

A yellow thunderstorm warning covers parts of Northern Ireland from 12:00 to 21:00 Tuesday, with up to 30mm of rain possible in an hour or two, plus strong winds and hail.
Scorched ground from weeks of hot, dry weather means any intense downpours could trigger flash flooding because water is more likely to pool and run off than soak in.
More than 30C is still expected in parts of southern and eastern England on Tuesday, while amber and yellow heat health alerts remain in force across much of England until 09:00 BST Wednesday.
That shift will not end the wider dry spell: the cold front moving south is unlikely to bring meaningful rain to the south-east, and forecasts point to a warmer-than-average, low-rainfall August.
47 consecutive dry days at Wisley in Surrey underscore the drought, with hosepipe bans already affecting more than 20 million people in England and Wales.