Hi, I have two 7 yr old healthy cats and live in London. I've had them only about 2 yrs. As I think most will know about, London's just had an unusually large amount of snow and more is on the way. Is it safe to let them out in this? I haven't so far as they tend to hop over walls etc and I don't know if they can navigate that safely. Any advice would be gratefully received. Thanks!