The weather will change wildly and frequently - that's why we talk about it all the time.
Stick to the BBC (Radio 4 or Radio 5) or the BBC website if you really want forecasts.
Due to some amazing foresight by this Government, most local libraries have a bank of on-line computers(free!). You can usually get on in the mornings and during school term-times. The BBC website gives detailed local forecasts.
Imho newspapers are no good at all for forecasts. Printed long ago and in some distant city.
Where are you going in the South-West?? And when? Many, many very beautiful areas but can be hilly, especially on the Cornish coast - nothing comes for free. Invest in some quality rain gear and forget messing about with forecasts; they'll be inaccurate anyway. Just look at the sky and smell the breeze.