Wow 30W.. you appear to have considerably more confidence in the weather forecasters than I do after a lifetime in aviation. Ring any two forecasters and get a different story. I planned to visit Farnborough today with family and friends and checked every available forecast... but early today we abandoned the visit based on three out of four forecasts of rain and thunderstorms. As I write (midday), the BBC is now saying "sunny intervals" whilst uk.weather.com is going for a 50% chance of precip and thunderstorms. Metcheck.com covers itself with "intermittent rain"!
I well remember trying to get a surface wind forecast whilst trying to decide whether to change runways at Heathrow - one forecaster promised a predominantly SW wind and 10 mins later another said it would be mainly SE!
UK ATC does it's very best in the circumstances and appropriate action is taken in severe weather but I suggest that there is a very long way to go before day-to-day planning becomes based on weather forecasts. Just imagine if flow control was introduced based on the forecasts for today.