Mate, check out this web site www.xcweather.co.uk for a good forecast of wind and weather situations in your area. Sounds like you might need to think about electrifying a bigger model, plenty of help here or closer to home www.rcmf.co.uk. A .40 sized trainer or scale cub/citabria/cessna etc
suitably electrified should be able to cope with winds up to 15mph, perhaps a bit more if you don't have any obstacles which cause turbulence.

Regards,
Andy