You've described the classic symptoms of poor signal strength, so it's probably either your aerial or the cabling that's causing the problem.
Have you actually taken a look up at your roof, to check that your aerial is still pointing in the right direction? (I once asked an AB member to do exactly that and he discovered that his aerial was lying on his lawn!).
The weather can play a part in the signal strength that you receive (as can the 11-year sunspot cycle, individual solar flares, interference from electrical devices in your house, similar interference emanating from your neighbours' homes and lots of other things) but, in the final analysis, you'll need to sort out your aerial (or possibly try a signal amplifier).
There's a more detailed response in my post here:
http://www.theanswerbank.co.uk/Technology/Question1447101.html