Hi Woodelf
It has been scientifically proved (using chaos theory) that it will NEVER be possible to provide accurate weather forecasts more than a few days ahead. That's why the Met Office and BBC websites only show detailed forecasts for a 5 day period. Even then the accuracy of the final day's forecast is far from guaranteed. Sites such as uk.weather.com, which offer 10 day forecasts, are really only looking at typical trends rather than offering true forecasts.
The furthest ahead that the Met Office 'forecasts' look is 30 days but they are really only providing an 'outlook' for the whole of the UK, indicating the possible whether trends around a particular period of the month. They can't provide specific forecasts for a particular part of the country on a specific day.
Relevant link:
http://tinyurl.com/ykvmhgz
Chris