Britain faces 'intense' thunderstorms today and tomorrow with a month's worth of rain forecast to fall on parched ground amid concerns 'severe' flash flooding could cut off villages.The Met Office extended yellow warnings across England and Wales as a band of slow-moving heavy showers and thunderstorms travelled northwards this morning.The first thunderstorm alert from 3am to 10pm today covers much of England including the South East, Midlands and North as well as northern and eastern Wales.Forecasters said up to 30mm (1.2in) of rain in less than an hour is expected in parts today, while up to 50mm (2in) could fall over two to three hours.The second thunderstorm warning from 6am to 10pm tomorrow will cover the whole of Wales as well a similar area of England, excluding London and the South West.Up to 30mm of rain falling in three hours can be expected fairly widely tomorrow and up to 50mm in a 12-hour period is anticipated in places.East-facing high ground could see more than 50mm fall in three hours tomorrow and more than 75mm (3in) over 12 hours. There are also warnings of hail of up to 2cm (0.8in).The Met Office amended the area of the two warnings this morning, with today's alert extended further north-westwards while removing it from parts of East Anglia. Two women shelter from the pouring rain under an umbrella in Westminster, central London, which is at risk of flash flooding Tomorrow's warning was also extended further north-westwards by meteorologists and will cover all of Wales while being removed from parts of eastern England.Met Office chief forecaster Steve Willington said: 'As we move into Wednesday there is a growing risk of heavy rain and thunderstorms, with warm and humid air helping to trigger 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.'On Thursday, slow-moving heavy and thundery rain may bring prolonged rainfall to some areas, increasing the risk of localised impacts.'There remains some uncertainty around where the heaviest rain will fall, so it is important to keep up to date with the latest forecast and warnings.'It follows hot weather in the UK which coincided with extremely dry conditions, with drought being declared in nearly three-quarters of England and the whole of Wales.The RAC said risks to drivers from slippery roads from rainfall are 'much greater right now as a result of the prolonged dry spell'.It added that oil, fuel and rubber deposits that have built up will now have been mixed together by light rain, instead of being washed away, which means drivers are at greater risk of skidding on greasy roads.London Mayor Sir Sadiq Khan said on X: 'From 3am, London is at risk of severe flash floods. Intense downpours could see up to 50mm of rainfall arrive in the space of just a few hours - almost the total average rainfall for August.'Don't be caught out - check your insurance covers flooding and see what more you can do to prepare.' He then shared a link to his website on how to prepare for flash flooding.The Met Office said the rain and thunderstorms this afternoon 'may be intense' – adding that there was a 'small risk of flooding and disruption', including possible damage to some buildings from floodwater, lightning strikes or hail. The first thunderstorm warning runs from 3am to 10pm today for up to 50mm (2in) of rain The second thunderstorm warning runs from 6am to 10pm tomorrow for up to 75mm of rain It added that spray and sudden flooding could lead to difficult driving conditions and some road closures.Large hail and frequent lightning are also possible before showers and thunderstorms drift northwards and ease during this evening.In tomorrow's warning, forecasters said there was a 'small chance of fast-flowing or deep floodwater causing danger to life'.They added: 'Some communities might become cut off if roads flood.'The Met Office has advised people to 'ensure moveable objects or temporary structures are well secured' before gusty winds arrive, including bins, garden furniture, trampolines, tents, gazebos, sheds and fences.Unsettled conditions may continue into Friday and the weekend, with further showers or longer spells of rain possible at times, alongside some drier and brighter periods.RAC road safety spokesman Rod Dennis said: 'While slippery roads from rainfall is nothing new, the risks to drivers are much greater right now as a result of the prolonged dry spell.'Oil, fuel and rubber deposits that have built up over many weeks will now have been mixed together by the light rain, instead of being washed away, which means drivers are at greater risk of skidding on greasy roads.'If heavier rain arrives, motorists may have to contend with the danger of flash floods in some areas.'For this reason, we urge drivers to reduce their speed in rainfall of any intensity and leave extra space behind the vehicle in front to reduce the chance of avoidable collisions.'The AA also urged drivers to prepare for rapidly changing road conditions.