Details of exactly where will see the worst impacts from these storms are likely to be uncertain until quite close to the time they break out, but National Severe Weather Warnings are being issued, broadly highlighting the most prone areas.

Warm air pushing in from the continent on Thursday will bring a slow-moving band of thunderstorms to parts of central and southern England and the West Country, and a Yellow warning for rain has been issued.

Chief Meteorologist Andy Page said: “The worst impacts are likely during the afternoon and evening on Thursday with the potential for 30-40 mm of rain to fall in an hour, and a chance of some isolated places seeing as much as 60-80 mm over two to three hours. Some will see frequent lightning and large hail as well. This could result in flash flooding, transport delays and dangerous driving conditions, especially on the M4 and M5.

“We’d advise anyone with outdoor plans over the next few days to keep updated with the forecast and warnings, and consider their plans if the risk of thunderstorms or heavy rain may affect them”.

As we go into Friday, the warm air over the UK will lead to the development of yet more thunderstorms, and another Yellow warning for rain has been issued. These thunderstorms will move from southern England and Wales towards Northern Ireland during the morning, becoming more scattered by the afternoon and evening.  In the torrential downpours as much as 20-30 mm of rain could fall in an hour with 60 mm in a few hours.

Kate Marks, Environment Agency flood duty manager, said: “Further heavy showers and scattered thunderstorms bring a risk of localised surface water and river flooding on Thursday and Friday. The main risk is across Southern England, East Anglia and parts of the South Midlands on Thursday, extending to parts of the North West on Friday. Urban areas are most likely to see the impacts.

“Throughout this period of unsettled stormy weather we will continue to work around the clock operating flood defences, clearing blockages in rivers and streams to ensure they flow freely, and supporting partners responding to any incidents of surface water flooding.

“ We remind people not to drive through flood water as just 30cm can move your car. The public can check our active alerts and warnings – which are updated every 15 minutes – online at www.gov.uk/check-flood-risk or by calling 0345 988 1188.”

Highways England’s Head of National Traffic Operations, Mike Ord, said: “We want everybody to arrive at their destination safely and without incident, and urge drivers to adapt their driving in wet weather. Rain makes it harder for tyres to grip the road and harder for drivers to see ahead – significantly increasing the chances of being involved in a collision.

“It generally takes at least twice as long to stop on a wet road as on a dry road. We recommend slowing down if the rain and spray from vehicles is making it difficult to see and be seen, keeping well back from the driver in front and, if you feel the steering becoming unresponsive, slow down gradually as it probably means that water is preventing the tyres from gripping the road.” 

RAC spokesman Pete Williams said: “Before setting out on a journey we would recommend you take a moment to check your windscreen wipers are working, ensure that you have good depth of tread on your tyres and they are correctly inflated, and use your sidelights in heavy rain.  Conditions could be hazardous on motorways and dual carriageways so reduce your speed to suit the conditions and leave plenty of space between your car and the vehicle in front. Remember, your stopping distance is significantly increased in the rain.  Avoid sharp acceleration and braking which could result in you losing control and getting in to a skid, and take extra care when overtaking large vehicles which will create lots of spray which reduces visibility.”

Richard Hancox, Duty Tactical Manager for Natural Resources Wales, said: “We know how devastating flooding can be to homes and businesses which is why we monitor river levels and provide up-to-date flood alerts to help protect communities wherever possible.

“Heavy rain is expected over the next few days which could increase the likelihood of river and surface flooding. We advise people to be cautious near rivers and on the roads and to keep updated on flood alerts via our website or by calling Floodline on 0345 988 1188.”

The risk of scattered heavy showers and thunderstorms tends to diminish over the weekend, with any activity being restricted to northern Britain.

Away from the thunderstorms, there will be plenty of fine weather with most areas seeing some sunshine over the next few days, although low cloud could continue to affect the eastern coastal areas.

Beyond the weekend, there will be a good deal of fine weather around, with the best of the sunshine in the northwest. However, scattered heavy showers and thunderstorms may continue to affect southern and western areas at times with dry and bright weather in between the showers. 

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