There are a number of sources for weather forecasts nationally and locally. It is probably fair to say that most pilots will not rely on any single source but rather look at multiple forecasts and decide on the most likely scenario on balance.
There are a number of links for weather forecasting websites on this page and also several general forecasts for North Staffordshire and the Peak District.
The use of forecasts on mobile devices is also very useful as is sharing information via Telegram groups; the PSA has such a group.
The list below is not exhaustive but it does provide the key sites that are more orientated toward free-flying activities.
A reasonable 'all round' strategy for planning purposes would be to review the forecasts from the following:
It is worth following local weather stations for up to the minute conditions and of course, information-sharing groups for information closer to the journey.
If all else fails try the piece of string outside of the window method 😊